Tag Archive for: NOAA

NWS Says La Niña Has Ended, Likely Impact on Weather

On March 9, 2023, the Climate Prediction Center of the National Weather Service (NWS) announced that La Niña conditions which persisted for 3-years have finally ended. But we are not shifting directly into El Niño. Instead, we’re entering a transitional phase. NWS expects neutral conditions to continue through the Northern Hemisphere into spring and early summer of 2023.

La Niña and El Niño represent opposite phases of what meteorologists call ENSO, the El Niño Southern Oscillation in the Pacific Ocean. They govern recurring climate patterns across the tropical Pacific and have a cascade of global side effects, says NWS.

The patterns shift back and forth irregularly every two to seven years. This past La Niña phase lasted three years, an unusually long time.

NWS predicts that ENSO-neutral conditions will continue through the spring. The weather service also predicts El Niño conditions to form during summer 2023 and persist through the fall.

Impacts on Weather

The oscillation brings predictable shifts in ocean surface and atmospheric temperatures. These shifts disrupt the wind and rainfall patterns across the tropics.

El Niño brings cooler, wetter conditions to the southern U.S. in winter months. It also brings stronger steering currents that can disrupt low-pressure systems coming off the coast of Africa that turn into hurricanes.

La Niña, on the other hand, usually means less disruption, more Atlantic storms, and deeper droughts in the southern U.S. But we’re finally putting the most recent La Niña behind us.

ENSO Influence on Atlantic and Pacific Hurricane Seasons

The continental United States and Caribbean Islands have a substantially decreased chance of experiencing a hurricane during El Niño and an increased chance of experiencing a hurricane during La Niña. These maps (by NOAA Climate.gov, based on originals by Gerry Bell) explain why.

Typical El Niño effects on Pacific and Atlantic seasonal hurricane activity.

Overall, El Niño contributes to more eastern and central Pacific hurricanes and fewer Atlantic hurricanes. Conversely, La Niña contributes to fewer eastern and central Pacific hurricanes and more Atlantic hurricanes – exactly the opposite.

Typical La Niña effects on Pacific and Atlantic seasonal hurricane activity.

Other Influences on Hurricane Formation: AMO

NOAA also says that other oscillations, such as the Atlantic Multi-Decadal Oscillation (AMO) also influence hurricane formation. The warm phase of the AMO is associated with warmer sea surface temperatures and high hurricane activity in the main development region of the Atlantic between Western Africa and the Caribbean.

“The hurricane activity in any given season often reflects a combination of the multi-decadal signals and ENSO,” says NOAA.

For More Information

For a fuller discussion of how El Niño and La Niña influence other aspects of weather worldwide, check out NOAA’s Climate.gov, especially the FAQ page.

Also, the Associated Press ran an interesting story this morning by Seth Borenstein. The headline: “La Nina, which worsens hurricanes and drought, is gone.”

Borenstein says NOAA gives El Niño a 60% chance of returning this fall. But there’s also a 5% chance that La Niña will return for an unprecedented fourth winter.

We should have more certainty in a few months.

Posted by Bob Rehak on 3/9/23

2018 Days since Hurricane Harvey

Why Hurricanes Often Track Like Boomerangs

Ever wonder why so many hurricanes track like boomerangs? They don’t all follow this pattern, of course, but when you look at the 1370 hurricanes between 1851 and 2006, a pattern clearly emerges.

From the US Department of Commerce book “Tropical Cyclones of the North Atlantic 1851 -2006.”

Interaction of Complex Systems

In my research, I found several possible explanations for the pattern above.

Harris County Meteorologist Jeff Lindner provided this explanation. “Many of the storms that form in the eastern or central tropical Atlantic tend to get pulled northward by mid-latitude troughs over the western Atlantic as they attempt to move westward. Storms that make it all the way across tend to happen only when strong ridges of high pressure are in place.” 

“Once a system is ‘captured’ by a mid-latitude trough, it will turn NW then N and then NE and E ahead of and along the trough axis. That’s why so many tracks are of this fashion over the open central and north Atlantic.”

Jeff Lindner, Harris County Meteorologist

Lindner added, “The further south a storm develops the less likely it is to be influenced by any sort of trough and a more westward track is then favored. Tracks into the Caribbean Sea from the east usually continue westward and those are what we tend to worry most about here along the Gulf Coast.”  

“It is very rare for storms to cross central America or Mexico due to the high mountains in this area. The mountains quickly destroy the low-level circulations. A few in history have survived the trek, but they are few,” said Lindner.

Shifts in Bermuda High

The mother of all high-pressure ridges in the Atlantic is sometimes called the Bermuda or Azores high. NOAA defines it as “a semi-permanent, subtropical area of high pressure that migrates east and west between Bermuda and the Azores depending on the season.”

Red arrow added to NOAA Image indicating migration of high between Bermuda and the Azores.

The Meteorology 101 blog says, “During the summer, [the Bermuda high] is located just off the east coast of the United States. The clockwise circulation around this high pressure area helps direct the path of hurricanes and helps determine where they will make landfall. … During the winter months, the Bermuda High is located farther east of the US towards the middle of the Atlantic Ocean. 

Depending on the Bermuda high’s location at any given time, it can block storms from going north. Or it can spin storms around in the boomerang pattern in the first image above. That’s because winds circulate in a clockwise fashion around high-pressure systems in the northern hemisphere.

Also note, sometimes gaps open in the high, letting storms slip north and get caught up in that clockwise circulation.

Highs Sometimes Block Storms from Curving North

HurricaneScience.org says, “Atlantic hurricanes typically propagate around the periphery of the subtropical ridge, riding along its strongest winds. If the high is positioned to the east, then hurricanes generally propagate around the high’s western edge into the open Atlantic Ocean without making landfall.”

“However, if the high is positioned to the west and extends far enough to the south, storms are blocked from curving north and forced to continue west, putting a large bulls-eye on Florida, Cuba, and the Gulf of Mexico.” This helps explain the wide spread of tracks on the left of the first image.

Influence of Trade Winds

This post from the National Oceanographic and Atmospheric Administration (NOAA) explains the relationship between the Sahara Desert and the formation of many hurricanes. Prevailing winds blowing from east to west (often called trade winds) come off the hot, dry Sahara Desert where they meet the cooler, wetter environment of the Atlantic Ocean west of Africa.

Prevailing global wind circulation patterns, courtesy of NASA

The prevailing winds in this latitude are so steady that in the days of sailing ships, mariners from Europe going to the Americas would first sail south to Africa. There, they would ride the reliable winds west to conduct commerce in the New World. Hence the name “trade winds.” The trade winds steer hurricanes, too.

In higher latitudes, the trade winds reverse direction. So sailors returning to Europe would sail north before returning to Europe and catch a tailwind home.

Opposing trade winds at least partially explain the boomerang pattern shown above.

If you ever get to Seville, Spain, make sure you visit the Archive of the Indies. There you will find the story of every Spanish treasure fleet that made the round trip between Europe and the Americas. I was struck by how many fleets sank in hurricanes while riding the trade winds.

Meteorology, or lack thereof, has influenced the fate of empires.

Coriolis Force

Many scientists also cite the Coriolis Force as a reason for why hurricanes try to drift north of dominant west-to-east winds. Frankly, the physics are beyond me. It has to do with the rotation of the earth at different speeds in different latitudes, and the rightward drift of objects (like hurricanes) not anchored to the earth while traveling over long distances. The Coriolis Force is also used to explain why hurricanes rotate in a counter-clockwise direction.

Posted by Bob Rehak on 8/31/2022 with input from Jeff Lindner, HCFCD

1828 Days since Hurricane Harvey

Hurricane Records

Today, I discovered a fascinating 49-page document produced by the National Weather Service, the National Hurricane Center, NOAA and the National Climatic Data Center. It contains hurricane records going back to 1851. It covers the deadliest, costliest and most intense U.S. tropical cyclones and other frequently requested facts. Unfortunately, it only goes through 2010. But the wealth of information on the period it covers more than makes up for that.

Like the Baseball Encyclopedia for Weather Geeks

It’s like the Baseball Encyclopedia for tropical storms…a must read for weather geeks and anyone who wants to impress out-of-town friends. Texas plays a prominent role in this chronicle.

From Page 8. Mainland United States tropical cyclones causing 25 or more deaths, 1851-2010. The black numbers are the ranks of a given storm on Table 2 (e.g. 1 is the deadliest all-time – the Galveston Hurricane of 1900). The colors are the intensity of the tropical cyclone at its maximum impact on the United States.

A look at the lists reveals striking facts. For instance:

  • Fourteen out of the fifteen deadliest hurricanes ranked Category 3 or higher intensity
  • Large death tolls resulted largely from storm surge 10 feet or higher
  • A large portion of the damage in some of the costliest storms resulted from inland floods caused by torrential rains
  • One third of the 30 deadliest hurricanes ranked category 4 or higher
  • Only seven of the 30 deadliest hurricanes occurred between 1985 and 2010 while more than two thirds of the costliest hurricanes occurred during the same period.

A Look Behind the Facts

All costs are adjusted for inflation, so that’s not the major issue. Migration is. 1990 Census data showed that 85% of U.S. coastal residents from Texas to Maine had never experienced a direct hit by a major hurricane. But we have more risk now because more than 50 million people have moved to coastal areas since then.

The study warns, “If warnings are heeded and preparedness plans developed, the death toll can be minimized. However, large property losses are inevitable in the absence of a significant change of attitude, policy, or laws governing building practices (codes and location) near the ocean.”

Filled with Tables, Maps and Insight

One of the most interesting features: maps that show the tracks of record setting storms during the entire period and during each decade.

Amaze your friends with trivia, such as:

  1. Average number of tropical cyclones per year AND how it has varied in different periods.
  2. Years with the most and least hurricanes and landfalls.
  3. Earliest and latest hurricane formations (hint: March 7 and December 31).
  4. Longest- and shortest-lived hurricanes.
  5. Lowest pressure in the Atlantic basin.
  6. Most hurricanes occurring in Atlantic basin at one time.
  7. Number of hurricanes in each month.
  8. Hurricane strikes of various categories by state.
  9. When hurricanes are most likely to strike different areas.
  10. Average return periods for hurricanes in different areas.
  11. Hurricane landfall CYCLES.

That last one really caught my eye.

Hurricanes tend to cluster in certain areas during certain decades!

Biggest Lesson Learned

The study concludes with another warning. “The largest loss of life can occur in the storm surge, so coastal residents should prepare to move away from the water until the hurricane has passed! Unless this message is clearly understood by coastal residents through a thorough and continuing preparedness effort, a future disastrous loss of life is inevitable.”

To read the full study, click here.

This is a genuine work of scholarship dished up in a way that makes it accessible to the general public. That takes some talent! Credits go to Eric Blake and Christopher Landsea of the NHC, and Ethan Gibney of the National Climatic Data Center.

Posted by Bob Rehak on 7/8/22 based on a study by NOAA, NWS and NCDC

1774 Days since Hurricane Harvey

Severe Weather Threat Increasing for Tomorrow, Up to 7″ Now Possible

Severe Weather, Flash Flood Likelihood Increasing for Monday Afternoon into Early Tuesday

Updated at 7:30 PM:

According to Jeff Lindner, Harris County Meteorologist, a powerful storm will move into Texas over the next 24 hours bringing multiple hazards to the area. The chances of severe weather and heavy rainfall by Monday afternoon and evening continue to increase. They are also expanding over a wider area. Since the original post, Harris County’s Meteorologist, Jeff Lindner has raised concerns about rises on the San Jacinto River West and East Forks to flood stage over the next few days. Rises on other creeks and bayous in Harris County also look likely, especially where we experience cell training and higher rainfall totals. Lindner advises to monitor weather closely on Monday and Monday night.

Outlook tomorrow for severe weather from the NWS Storm Prediction Center.

Higher Likelihood of Severe Weather Including Tornados Starting Monday Afternoon

There were some doubts yesterday about the likelihood for supercells to develop. But as we get closer to the storm’s arrival and certainty increases, supercell formation looks increasingly likely. “All severe modes will be in play including tornadoes, large hail, and damaging winds,” says Lindner. “There could be a few strong tornadoes, especially for locations north of I-10.” Yesterday, the main likelihood was north of SH105.

The National Weather Service Storm Prediction Center has expanded the enhanced risk (3 out of 5) outline to include more of Southeast Texas. The severe threat will begin in the mid-afternoon hours on Monday and continue into the late evening hours.

6-7 Inches, Flash Flooding Possible 

While the heaviest rainfall will likely occur over North Texas, the potential for high-precipitation supercells to develop and train across Southeast Texas is increasing for Monday afternoon and evening. As the front slows over Southeast Texas Monday night, Lindner expects the severe threat to gradually shift toward heavy rainfall and possible flash flooding throughout the night.

The greatest threat will generally be along and north of I-10. A slow-moving line of supercells will raise the flash-flood threat. If you get caught under one that’s training across your area as we saw back in January, be prepared.

Lindner has virtually doubled his rainfall predictions since yesterday. Instead of widespread 0.5-2 inches across the area, he now sees widespread 3-4 inches. And whereas yesterday he saw isolated rainfall totals up to 4 inches, today he estimates up to 6-7 inches.

Hourly rainfall rates of 2-3 inches will be possible leading to rapid onset flash flooding over urban areas. Street flooding will be the primary threat, but under corridors of excessive rainfall, significant rises on creeks and bayous will be possible.

Jeff Lindner, Harris County Meteorologist

In an update at 7:30 PM Sunday night, Lindner specifically mentioned the possibility of the East and West Forks of the San Jacinto rising to flood stage if we receive the higher rainfall totals in the forecast.

The NWS Weather Prediction Center has upgraded the area north of the I-10 corridor to a moderate risk for flash flooding.

National Weather Service outlook tomorrow for excessive rainfall.

Monday afternoon and evening will be active over the area. So have multiple ways to receive warnings. Make sure you have fresh batteries in your weather radio and flashlights; it could be a long night.

Putting Forecast in Perspective

To put this in perspective:

  • The supercells that spawned tornadoes over Kingwood in January dumped approximately 5 inches of rain. I talked with a lady on Facebook this morning whose home was destroyed by a tornado in that storm. She said she received warnings seconds before the tornado struck. She barely had enough time to get to an interior hallway before her home started crumbling around her.
  • The May 7th, 2019, storm that flooded more than 200 homes in Elm Grove dumped 7 inches of rain. But less than 20% of the floodwater detention capacity on Woodridge Village had been built at that point.
  • The City announced at 5:15 this afternoon that it will lower Lake Houston by 1 foot starting tonight. A forecast greater than 3 inches triggers the Lake Houston lowering protocol.

How To Get Warnings

NOAA broadcasts warnings on weather radio in a continuous loop during emergencies.

The National Weather Service lets you sign up for watches and warnings for your address.

Harris County’s Flood Warning System also lets you sign up to receive rainfall or flooding alerts for your location. The site also contains maps that show real-time rainfall, and river-channel monitoring and forecasting at gages throughout the region.

USGS has a web app called Water On the Go that shows water elevations at flood gages wherever you go in Texas.

Harris County Flood Control District’s Storm Center can connect you to a wide variety of preparedness articles and ways to summon help in an emergency.

A number of companies offer good apps for cell phones that offer warnings. I especially like one called Dark Skies that bills itself as “hyper-local” weather. It frequently tells me to the minute when a storm will arrive at my exact location…wherever I am.

You can also find links to dozens of other weather related apps and sites on my Links Page. Check them out before the storm arrives. You never know when a storm will knock out a web site, a cell tower, or power. So be prepared with multiple backups.

Posted by Bob Rehak on 3/20/2022 based on input from the NWS, HCFCD and City of Houston

1664 Days since Hurricane Harvey

Big Picture

It’s always nice to start the new year by looking at the big picture. And big pictures don’t get much bigger than this. The image below comes from NOAA’s Global Data Explorer. It shows sea surface temperature anomalies in the Pacific and Atlantic. Reds show areas with warmer than normal temperatures. Blues are cooler.

Sea surface temperature anomalies from 12/20/21 to 12/26/21. Source: NOAA.

Degrees of Variation

The dark red areas are a whopping 4-5 degrees Celsius above normal. The dark blues are 3-4 degrees Celsius below normal. It takes 1.8 degrees Fahrenheit to equal 1 degree Celsius. So in terms of the temperature scale that most people in the US use, that’s up to 9 degrees warmer and 7.2 degrees cooler – a 16.2 degree spread.

This helps to explain the record warm December we just had. Houston is in that band of red that stretches across the northern hemisphere. Also notice how red the Gulf of Mexico is.

According to the EPA, an increase in sea surface temperatures can lead to an increase in the amount of atmospheric water vapor over the oceans. “This water vapor feeds weather systems that produce precipitation, increasing the risk of heavy rain and snow.” And we just had extreme snowfalls from the Sierras to the Rockies.

Role of Ocean Currents

Ocean currents help distribute this moisture around the world. According to NOAA, “almost all rain that falls on land starts off in the ocean.”

The world’s major ocean currents distribute heat and moisture across the globe. Source: NOAA.

“Ocean currents act much like a conveyor belt, transporting warm water and precipitation from the equator toward the poles and cold water from the poles back to the tropics,” says NOAA. “Thus, ocean currents regulate global climate, helping to counteract the uneven distribution of solar radiation reaching Earth’s surface. Without currents in the ocean, regional temperatures would be more extreme—super hot at the equator and frigid toward the poles—and much less of Earth’s land would be habitable.”

Cyclical Variation

Sea surface temperatures vary in cyclical, but irregular patterns (roughly every 3-6 years). Right now, we are under the influence of a La Niña pattern, that recurs every few years and can last as long as two years. This page on NOAA’s site explains what causes the changes. They often start with ocean currents veering off course for a period of time or stronger than normal trade winds.

The World Meteorological Association gives this La Niña an 80% chance of lasting through this spring before returning to normal (neutral) conditions.

Posted by Bob Rehak on 1/1/22

1586 Days since Hurricane Harvey

Government Moves to Make Climate Information, Decision Tools More Accessible

Last week, the White House announced a government-wide initiative to make climate information more accessible and actionable. The effort targets individuals and communities hit by flooding, drought, wildfires, extreme heat, coastal erosion, and more.

Not everyone agrees on climate change. But we have all observed what happens when people fail to sufficiently heed climate risk. This effort to make climate information and science more accessible to the public is long overdue and welcome.

A better understanding of climate risks will empower communities to better prepare for them.



From Climate.gov’s Data Snapshot Page

For instance, did you know that La Niña—the cool phase of the El Niño-Southern Oscillation climate pattern—has returned to the tropical Pacific this month. NOAA gives it an 87 percent chance to last through Northern Hemisphere winter. Here’s what that could mean for us.

List of New Websites, Reports, Initiatives

Below are 15 websites, reports and initiatives that may help those making important decisions about starting a business, buying a home, or protecting their communities.

  • Extreme heat hot spots 
  • Areas impacted by wildfire smoke
  • NOAA’s redesigned Climate.gov. Upgrades to this website will better connect Americans to climate explainers, data dashboards, and classroom-ready teaching resources. It now better provides the public with clear, timely, and science-based information about climate. Climate.gov’s Global Climate Dashboard gives a data-driven readout on the state of the climate system with public-friendly explainers and answers to frequently asked questions. Climate.gov also provides access to commonly requested climate data and tools hosted by NOAA’s National Centers for Environmental Information.
    • Using an artificial intelligence platform to improve the search tool, allowing queries based on location so that users can find city and state-specific maps and data;
    • Cross-linking content to highlight all available resources sitewide that are relevant to each visitor’s unique interests;
    • Improving the mobile experience on tablets and smartphones; and
    • Redesigning pages with user experience and accessibility in mind.
  • These efforts build on FEMA’s announcement earlier this year of nearly $5 billion in funding available for community projects to prepare for extreme weather.
  • An Office of Science & Technology Policy (OSTP), NOAA, and the Federal Emergency Management Agency (FEMA) report on expanding and improving climate information and services for the public.
  • A Federal Geographic Data Committee report focusing on opportunities to enhance climate planning.
  • A FEMA initiative will assess National Flood Insurance Program standards to help communities update minimum floodplain management standards—which makes them eligible for federal flood insurance. The standards have not been substantially updated since 1976. But through a Request for Information, FEMA will gather stakeholder input to make communities more resilient while saving lives, homes, and money.
  • A report titled “Opportunities for Expanding and Improving Climate Information and Services for the Public,” charts a course for expanding accessibility and use of the federal government’s climate information to support all communities, including those who have been historically underserved, on climate planning and resilience activities. The report lays out opportunities to: 
    • Focus climate services on the challenges that pose the greatest risks and opportunities
    • Foster interagency coordination and public-private partnerships
    • Enhance the usability of climate services for all Americans
    • Strengthen core science capabilities
  • Another report builds off of the federal government’s existing information, tools, and services, such as the interagency U.S. Climate Resilience Toolkit; FEMA’s National Risk Index for Natural Hazards; and the AirNow Fire and Smoke Map.
  • A third report titled “Advancing the Nation’s Geospatial Capabilities to Promote Federal, State, Local, and Tribal Climate Planning and Resilience” addresses Federal Mapping Services for Climate Planning
  • The National Science Foundation will leverage its Societal Experts Action Network (SEAN) to support the work of National Climate Task Force’s Interagency Working Groups on Drought, Flood, Coastal, Extreme Heat, and Wildfire Resilience.

This information is a dream come true for weather wonks, science teachers and flood victims.

Posted by Bob Rehak on 10/17/2021 based on information provided by the White House, and thanks to FEMA’s Diane Innes Cooper for the heads up.

1510 Days since Hurricane Harvey

Ida Now Hurricane, Predicted to Intensify to Category 4, Take Aim at New Orleans

As of 3 p.m. CDT, the National Hurricane Center indicated Tropical Storm Ida had intensified into a hurricane about to cross over the western tip of Cuba. They warn that it could turn into a category 4 hurricane. It is currently predicted to cross over Louisiana, dump up to 20 inches of rain, and produce 15 feet of storm surge on Sunday.

Warnings Now In Effect

The NHC has also posted several warnings. They include:

  • Storm Surge Warning from Rockefeller Wildlife Refuge in Louisiana to the Mississippi/Alabama border.
  • Hurricane Warning for the coast of Louisiana including Lake Pontchartrain and Metropolitan New Orleans.
  • Tropical Storm Warning from the mouth of the Pearl River to the Mississippi/Alabama border.
  • Tropical Storm Warning for the coast of Louisiana from west of Intracoastal City to Cameron.
Hurricane Ida over the western tip of Cuba as of 3PM Houston time on 8/27/2021

Rapid Intensification

According to the National Hurricane Center, radar indicated a closed eye 24 nautical miles wide. Recon aircraft measured winds at 70 knots – hurricane intensity – at 3 PM Houston time.

Once Ida moves past western Cuba and into the southeastern Gulf of Mexico, it will be moving through very warm waters, low wind shear, and a moist low- to mid-level atmosphere. These conditions should result in rapid strengthening during the next 24 to 36 hours.

In fact, with the higher initial wind speed, the intensity guidance has significantly increased.

Models now predict Ida will reach category 4 intensity. The NHC forecast explicitly calls for rapid intensification during the next 24 to 36 hours.

National Hurricane Center

Some fluctuations in intensity are possible as Ida nears the northern Gulf coast due to possible eyewall replacement cycles. Models also call for Ida’s wind field to expand while it moves over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a large and powerful hurricane will impact portions of the northern Gulf coast by late this weekend and early next week.

Ida has wobbled a little right of the previous track, but the longer term motion continues to be northwestward at about 14 mph.

Tracking Quickly Toward Louisiana Then Slowing

Steering currents push Ida northwestward across the Gulf this weekend. But Ida after landfall they will also slow northward motion and cause the system to turn northeastward.

Key Messages

However, remember not to focus on the exact details of the track. Storm surge, wind, and rainfall impacts will extend far from the center, says the NHC.

1. Life-threatening storm surge and hurricane conditions will continue through tonight in portions of western Cuba. Life-threatening heavy rains, flash flooding and mudslides are expected across Jamaica, the Cayman Islands, and western Cuba, including the Isle of Youth.

2. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana and Mississippi within the Storm Surge Warning area. Extremely life-threatening inundation of 10 to 15 feet above ground level is possible within the area from Morgan City, Louisiana, to the Mouth of the Mississippi River. Interests throughout the warning area should follow any advice given by local officials.

3. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of Louisiana. Hurricane-force winds are expected Sunday along the Louisiana coast, including metropolitan New Orleans, with potentially catastrophic wind damage possible where the core of Ida moves onshore. Actions to protect life and property should be rushed to completion in the warning area.

4. Ida is likely to produce heavy rainfall later Sunday into Monday across the central Gulf Coast from southeast Louisiana to coastal Mississippi and Alabama, resulting in considerable flash, urban, small stream, and riverine flooding impacts. As Ida moves inland, flooding impacts are possible across portions of the Lower Mississippi and Tennessee Valleys.

Story of the Storm in Picture

Confidence in track is increasing. Ida should reach the Louisiana and Mississippi coasts by Sunday afternoon.
…but tropical-storm-force winds should arrive by Sunday morning.
Most of the Houston area only has about a 10-30% chance of experience tropical-storm-force winds.
And we have practically no chance of excessive rainfall that could create flash flooding.
Portions of Louisiana, however, will like see 15-20 inches of rain.
But the biggest threat by far to our neighbors will come from storm surge. Portions of the delta could see as much as 15 feet above ground level.

Prays for our neighbors. And thank God that we’re on the dry side of this storm. It should hit on August 29th, the fourth anniversary of when Hurricane Harvey triggered massive evacuations in the Lake Houston Area.

Posted by Bob Rehak on 8/27/2021

1459 Days since Hurricane Harvey

TD9 Dumping Up to 20 Inches on Caymans, Hurricane Likely in Gulf by Sunday

As of this 11 a.m this morning, the National Hurricane Center (NHC) says that Invest 99L has turned into Tropical Depression 9 (TD9). Satellite imagery now shows circulation in the area of low pressure over the west-central Caribbean which I posted about yesterday. Cuba and the Caymans have already issued tropical-storm warnings. Extremely heavy rainfall is expected there. And the storm should strengthen into a hurricane by Sunday. Yet the effects on the Houston region will like be felt offshore and in coastal areas.

Center of circulation starting to form. NOAA Satellite image as of 9:50 a.m. CDT on August 26, 2021.

TD9 Current Intensity and Location

The initial intensity of TD9 as of 11 a.m. Houston time is approximately 35 mph with gusts to 40. An Air Force Reserve reconnaissance aircraft is scheduled to be in the system later this afternoon to provide more information on the system’s structure and intensity.

TD9, now located just south of Grand Cayman, is moving northwestward at 13 mph. The National Hurricane Center (NHC) indicates the system should move steadily northwestward. That would bring the center near or over western Cuba late Friday, over the southeastern Gulf of Mexico on Saturday, and approaching the US Central Gulf coast on Sunday.

Models are in relatively good agreement regarding the track forecast for TD9. However, error at Day 4 is around 175 miles, so don’t focus on details of the long-range track forecast. Some shifts in the track are likely until the system consolidates and becomes better defined, according to the NHC.

The cone of uncertainty for TD9 at this point stretches all the way from Houston to Mississippi. Every point within the cone has an equal chance of being hit.

TD9 will move over warm waters of the northwestern Caribbean during the next 24-36 hours. This, in combination with low vertical wind shear and a moist environment, should allow for steady strengthening.

Rapid Intensification Likely in Next 48 to 72 Hours

NHC forecasts TD9 to become a tropical storm later today or tonight. It could approach hurricane strength as it passes western Cuba.

Once the system moves into the Gulf of Mexico, conditions support additional strengthening. The NHC forecast explicitly shows rapid intensification between 48 and 72 hours for now.

The NHC intensity forecast brings the system near major hurricane strength when it approaches the northern Gulf coast on Sunday.

NATIONAL HURRICANE CENTER

Most global models show significant intensification of TD9 over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a strengthening tropical cyclone will be moving over the Gulf this weekend.

Key Messages

1. Tropical storm conditions are likely in the Cayman Islands tonight and western Cuba Friday, with dangerous storm surge possible in western Cuba.

2. The system will likely produce life-threatening heavy rains, flash flooding and mudslides across Jamaica, the Cayman Islands, western Cuba, and portions of the Yucatan Peninsula.

3. This system should approach the northern Gulf Coast at or near major hurricane intensity on Sunday, although the forecast uncertainty is larger than usual since the system is just forming. There is a risk of life-threatening storm surge, damaging hurricane-force winds, and heavy rainfall Sunday and Monday along the northern Gulf Coast from the Florida Panhandle to the upper Texas coast, with the greatest risk along the coast of Louisiana. Interests in these areas should closely monitor the progress of this system and ensure they have their hurricane plan in place.

Most of the Houston area has a 30-40% chance of experiencing tropical-storm-force winds from this storm.
Tropical-storm-force winds could arrive by early Sunday morning.

Likely Hazards in Islands and Mainland

The main hazards associated with TD9 as it passes Cuba and the Caymans will be:

STORM SURGE:

2 to 4 feet above normal tide levels in areas with onshore flow. Near the coast, the surge will be accompanied by large and destructive waves.

WIND:

Tropical storm conditions are expected in the Cayman Islands tonight and Cuba on Friday.

RAINFALL:

The depression is expected to produce total rainfall accumulations of 6 to 10 inches with maximum totals of 15 inches across Jamaica. Rainfall totals of 8 to 12 inches with isolated maximum amounts of 20 inches are expected across the Cayman Islands, western Cuba, and the northeast Yucatan Peninsula. These rainfall amounts may produce life-threatening flash floods and mudslides. Rainfall from this system is likely to begin impacting portions of the central U.S. Gulf Coast by early Sunday.

SURF:

Swells generated by this system will begin affecting Jamaica, the Cayman Islands and Cuba tonight and Friday. These swells are likely to cause life-threatening surf and rip current conditions.

Lindner Cautiously Optimistic At This Point

Jeff Lindner, Harris County meteorologist believes, “Impacts along the upper TX coast will likely be increasing swells and minor coastal flooding at high tide late this weekend into early next week.”

Monitor forecasts closely in case things change and be prepared for anything. We still won’t reach the peak of hurricane season until mid-September.

Statistical peak of Hurricane Season is September 10.

Posted by Bob Rehak at noon on 8/26/2021 based on information from NHC and HCFCD

1458 Days after Hurricane Harvey

So Far, 99L Headed Toward Gulf Along Same Track as Harvey

Jeff Lindner, Harris County’s meteorologist, forecasts a potential hurricane threat for the western and northwestern Gulf of Mexico early next week. And it’s following the same track as Harvey – almost four years later to the day.

Current Location of 99L in South-Central Caribbean

A tropical wave currently designated 99L and moving westward in the Caribbean off the coast of Columbia still has no center of circulation. However, global models indicate that it will continue to develop over the western Caribbean Sea either Friday or Saturday and move into the south-central Gulf of Mexico over the weekend.

Area of Investigation 99L is that large blob between the eastern tip of Cuba and the northern coast of Colombia.
99L on left should reach the southern Gulf by this weekend.

Still a Wide Range of Potential Tracks for 99L

There has been a significant shift during the last 24 hours to the right (east). The majority of the models now show 99L heading in the direction of the northwest Gulf of Mexico. However, models also show a wide range of potential tracks from northern Mexico to the Mississippi coast. 

The black line is the most likely track but uncertainty remains high.

So, a fair amount of uncertainty exists in the forecast, especially since there is such spread in the ensemble guidance. The lack of a defined surface center at the moment increases that uncertainty. 

Hurricane Harvey’s track in 2017. Note the similarity in area of origin and projected paths. Also note where Harvey intensified.

This weekend will be the fourth anniversary of Harvey. It’s eerie to note the similarities between that storm and this one.

Intensification Very Likely

Conditions over the Gulf of Mexico appear to be favorable for intensification. 

Nearly all global models see 99L turning into a hurricane. Some see it turning into an intense hurricane in the Gulf by early next week.

Lindner warns that It is too early to start discussing impacts because of the uncertainty on the track. However, he does see increasing tides and 10-15 foot waves from Sunday into Monday. Rain chances will increase starting today and remain high into the weekend. 

“Obviously,” says Lindner, “the forecast and potential impacts will have significant changes as the track become more clear in the coming days.”

Residents and interest along the TX and LA coast should review hurricane plans and make sure hurricane supplies are fully stocked. Monitor forecasts closely and frequently.

Posted by Bob Rehak on 8/25/2021 based on information from HCFCD, NOAA, NHC and Tropical Tidbits

1457 Days since Hurricane Harvey

Atlantic Basin Heating Up with Potential Tropical Activity

As we approach the 4th anniversary of Hurricane Harvey, the Atlantic basin is currently heating up with tropical activity. As remnants of one hurricane washing across New England, two more areas of concern move toward the Northeast. A third is heading toward the northwest Caribbean. It’s still too early to tell exactly where these storms will make landfall. But the presence of so many tropical disturbances signals the need to stay alert to daily weather forecasts.

Each of these storms has a 40-60% chance of tropical formation.

Five Day Outlook for Tropical Activity

8 PM outlook on 8/23/2021 indicates the storms heading toward the NW Caribbean have a 50% chance of tropical formation in the next five days. That’s up from 30% this morning.

Retreat of High-Pressure System Over Texas

National Hurricane Center (NHC) forecasts a tropical wave over the eastern Caribbean Sea will form a broad area of low pressure over the southwestern Caribbean Sea by late week. Thereafter, environmental conditions favor gradual development while the system moves west-northwestward to northwestward over the northwestern Caribbean Sea.

In addition to that, another major low pressure area over Mexico and the Bay of Campeche could move into the Gulf by this weekend though no tropical activity is forecast at this time.

Note massive low pressure system moving into Gulf.

Jeff Lindner, Harris County meteorologist, warns that as the high pressure ridge currently sitting over Houston begins to retreat north by Wednesday, “A series of tropical waves and disturbances will move from east to west across the US Gulf coast and into coastal TX from mid week onward. With a significant influx of Gulf moisture, showers and thunderstorms will return as early as Wednesday across much of the area and last likely into next week. Locally heavy rainfall will become an increasing threat by late week and this weekend with tropical moisture firmly in place over the region.”

Historical Norms for Late August

NOAA’s Climate Center shows that the projected path of the current areas of concern should follow historical norms for this time of the year.

This diagram shows the most likely areas for formation for hurricanes in August and their prevailing tracks. Source: NOAA’s Climate Center.

This is one of the reasons why.

Current sea surface temperatures in the Gulf are running 1.5 to 2+ degrees degrees above normal for the next seven days, with the warmer areas nearer the Texas Coast.

Historical Intervals Between Major Hurricanes

NOAA’s Climate Center shows the average interval for major hurricanes striking the Houston area is about every 25 years.

NOAA’s Climate Center also tracks the average return period for MAJOR hurricanes at various points along the coastline. They show that the Houston area can expect on average one major hurricane about every 25 years.

Of course, a hurricane doesn’t have to be major to cause major damage. Allison and Imelda were just tropical storms. And averages are just that – averages. Ike in 2008 and Harvey in 2017 each attained major hurricane status and hit Houston within 9 years of each other.

Posted by Bob Rehak on 8/23/2021 based on information from NHC and HCFCD

1455 Days since Hurricane Harvey