Tag Archive for: NOAA

Don Becomes First Hurricane of 2023 Atlantic Season

At 2:00 PM EDT on 7/22/23, the National Hurricane Center announced that Tropical Storm Don became Hurricane Don, the first Atlantic storm to achieve hurricane-force winds this year. Not only did Don form earlier than usual, it formed farther north than usual – between New England and Europe. Hurricanes hardly ever form in that area this early in the Atlantic hurricane season.

Hurricane Don’s Current Location

Location of Hurricane Don on is parallel with New Jersey. NOAA gives the orange area a 60% chance of formation in the next 7 days.

Hurricane Don’s Expected Track

NHC expects Don to decrease in strength to a tropical storm on Sunday and a tropical depression on Monday as it turns toward Europe.

Higher than Normal Sea Surface Temps Contribute to Early Formation

Warmer than normal sea surface temperatures played a role in the intensification of Don. Note the dark brown to black areas off the coasts of New England and Newfoundland. Those colors indicate a whopping 4 to 5 degrees centigrade above normal. That equals 7-9 degrees Fahrenheit.

No Hurricanes Reported Forming That Far North This Early

NHC shows that in the 165 years between 1851 and 2015, no other hurricane formed as far north as Don during this 10-day period.

From National Hurricane Center Climatology page.

Average Dates of Formation for Named Storms

Usually, the Atlantic Basin doesn’t see its first named hurricane until August 11. So Don is a month ahead of schedule on that count.

Dates of named storms from National Hurricane Center Climatology page.

Don is no threat to the Houston area. But Don’s timing may give us a clue to the type of hurricane season this will be. Both Colorado State and NOAA predicted slightly above average hurricane seasons this year.

The fourth tropical storm of the year doesn’t usually happen until August 15. And the first hurricane doesn’t usually happen until August 11.

El Niño Not a Factor in Don’s Formation

It takes the alignment of seven ingredients to form tropical cyclone. NOAA lists warm seas as #2. And we certainly have that around the world this year year, as you can see in the anomaly map above.

Wind shear from El Niño would not play a factor in deterring hurricane formation as far north as Don OR this early in the season, says Harris County’s meteorologist Jeff Lindner. “El Nino has little to no influence on our weather during the summer months (June-September),” says Lindner.

“The majority of El Nino’s influence on southern plains and Texas weather is during the fall, winter, and spring (October-May). This time of year we tend to be controlled by the sub-tropical highs around 30º N and/or the influences of the tropics from the Gulf of Mexico. This particular year the Sonoran sub-tropical high over the SW US and northern MX had thus far been the main controlling factor in our weather and El Nino has little impact on that.” 

Lindner concluded, “The wind shear associated with El Niño is mainly across the southern Gulf of Mexico, much of the Caribbean Sea, and the western deep tropical Atlantic. However, wind shear thus far this hurricane season has not been overly impressive for an El Nino summer and there are some suggestions that the very warm Atlantic waters may be lessening the impacts of El Nino and its wind shear in the Atlantic basin.”

We’re into uncharted territory, so to speak. This is where it gets interesting.

Posted by Bob Rehak on 7/23/2023

2155 Days since Hurricane Harvey

Necessary Ingredients for a Tropical Cyclone

This morning I visited the National Hurricane Center website to see the latest tropical developments. The Houston Area has nothing to worry about at the moment. But while I was on the NHC website, I stumbled on an incredible resource. It discussed – among other things – the necessary ingredients for a tropical cyclone. It’s called the Mariner’s Tropical Cyclone Guide, updated by Dylan Flynn in May 2023.

A Treasure Trove of Information about Tropical Systems

The title sells this electronic booklet short. It’s true that the last quarter of this 86 page booklet discusses how to navigate ships and boats near tropical cyclones. But the rest is a primer on tropical systems themselves. The booklet has four chapters:

  • Tropical Cyclone Basics
  • Climatology
  • Monitoring Tropical Cyclones
  • Tropical Cyclone Evasion

Although the book is targeted at Navy and Merchant Marine personnel, the general public will find the first three parts both informative and educational. The writing is clear, crisp, and concise. And the illustrations are illuminating. Overall, a quick read.

One of the most fascinating discussions started on page 12.

Necessary Ingredients for Development and Intensification

Flynn lists seven environmental conditions necessary for tropical cyclones to form and thrive. Eliminate one, says Flynn, and the whole system starts to break down.

  1. A pre-existing surface disturbance with thunderstorms: Tropical cyclones rely on a build-up of heat energy above them to grow and develop. A thunderstorm complex acts as a vertical transport mechanism for heat, moisture, and the cyclonic turning of winds into the upper levels of the atmosphere. This vertical transport helps tropical cyclones develop.
  2. Warm ocean: Tropical cyclones draw on the heat energy stored in the ocean. Sea surface temperatures of at least 80ºF are needed to support development and intensification. Evaporation of this warm water begins the process of energizing the atmospheric column. The warm seas should extend at least 60 m deep, as the strong winds of a tropical cyclone cause a turbulent sea that mixes the warm surface water with cooler, deeper water.
  3. Low vertical wind shear: Tropical cyclones rely on a vertically stacked structure to grow or maintain intensity. The ideal tropical cyclone has its upper-level circulation directly above the low-level circulation. Changes in environmental wind speed or direction with height will tilt the vertical structure. This tilting inhibits growth and may cause the system to decay.
  4. Unstable atmosphere: Rising air is needed to warm the tropical cyclone core, and an unstable atmosphere is necessary to support rising air.
  5. High atmospheric moisture content: Cloud formation is limited if the atmospheric column is too dry. Rising air will cool but struggle to reach the low dew point. The environment is often stable for dry parcels of air but unstable for moist air.
  6. Upper-level outflow: An exhaust mechanism is needed above a system to perpetuate the strong upward motion. This upper-level mass removal causes the pressure at the surface to drop. As a system develops, low-level cyclonic flow pulls mass toward the center. The flow then turns upward as intense vertical motion associated with thunderstorms. This process is known as “the in-up-and-out” circulation. Without a method to dispose of the mass above a tropical cyclone, low-level converging flow toward the center will halt as the system suffocates.
  7. Adequate Coriolis force: Due to the earth’s rotation, the Coriolis force causes tropical cyclones to spin counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. This spin is a critical component for development and intensification. Tropical cyclones rarely develop within 5 degrees of the equator, where this force is weakest. See gap in illustration below.

Other Fascinating Discussions

This is just one of dozens of fascinating topics in Flynn’s booklet. Among other things, Flynn discusses:

  • The exact meaning of terms used by NOAA and the National Hurricane Center. For instance, do you know the difference between a potential tropical cyclone, tropical cyclone and tropical depression? See pages 7-8.
  • How tropical cyclones dissipate and transition into extratropical storms. Page 14.
  • The size of the impact area for tropical cyclones. Page 15.
Largest and smallest tropical cyclones on record. Source: NOAA’s Mariner’s Tropical Cyclone Guide by Dylan Flynn. NM stands for nautical miles (about 6,076 ft).
  • What 50 foot waves look like to a sail drone from inside the eye of hurricane. Page 22.
  • How dangers differ in different areas around cyclones.
  • Seasonal variations and the influence of El Niño.
  • Environmental steering currents for cyclones.
  • How to interpret NOAA’s technical charts and tables, such as wave heights/intervals, wind forecasts, etc.

The general public and weather enthusiasts will find a boatload of useful information in this booklet, not just the necessary ingredients for a tropical cyclone.

Posted by Bob Rehak on 7/22/2023

2153 Days since Hurricane Harvey

Hurricane Season Above Average So Far

NOAA’s National Hurricane Center issues a monthly Atlantic Tropical Weather Summary during hurricane season. For June 2023, it shows above normal tropical cyclone activity and and above normal accumulated cyclone energy (ACE) for the North Atlantic, Caribbean and Gulf of Mexico.

#4 for Year and Counting

Three named tropical storms (Arlene, Bret, and Cindy) formed in the basin during June. The report also shows an unnamed storm in January, that in retrospect appears to have been tropical in strength.  

Bret brought tropical-storm-force winds to portions of the Lesser Antilles, while Arlene and Cindy remained over open water and did not impact land.  

So far, seasonal activity has been above average based on the 30-year climatology (1991-2020), where a named storm typically forms about once every year in June. 

peak of hurricane season
Timing of hurricanes in the last hundred years shows peak at September 10.

In terms of Accumulated Cyclone Energy (ACE), which measures the strength and duration of tropical storms and hurricanes, activity in the basin so far in 2023 has also been above average compared to the long-term (1991-2020) mean.

Reports on individual cyclones, when completed, are available at the National Hurricane Center website.

Summary Table

Name                       Dates              Max Wind (mph)

———————————————————–

Unnamed STS*                                              

TS Arlene                  1-3 Jun                 40

TS Bret                  19-24 Jun                 70

TS Cindy                22-26 Jun                 60

———————————————————–     

* An unnamed subtropical storm formed in mid January. Exact dates and maximum winds will be provided once the post-storm analysis is complete.

As of this writing on 7/5/23, NHC predicts NO tropical storm activity anywhere in the Atlantic basin for the next seven days.

Predictions Vs. Actual

In May, both NHC and Colorado State University predicted that this tropical storm season would have about normal hurricane activity. Both sources cited conflicting trends as the basis for their predictions. We currently have above-normal sea-surface temperatures throughout most of the Atlantic basin. We also are now under the influence of an El Niño, which tends, in this latitude, to produce wind shear that discourages cyclone formation.

To improve predictions, NOAA has made a number of changes in reporting at the National Hurricane Center. They include new, improved models for hurricane forecasts and storm surge, longer-range hurricane outlooks, an excessive rainfall outlook, inundation mapping down to the street level, and improved data-collection technologies.

Posted by Bob Rehak on 7/5/2023

2136 Days since Hurricane Harvey

NHC Predicts Near Normal Hurricane Season

Hurricane season starts this week. Offsetting factors, some of which would call for an above-normal hurricane season and others of which would call for a below-normal season, led forecasters at the NOAA Climate Prediction Center to split the difference in their seasonal outlook.

They are giving almost equal probabilities to average, above-average, and below-average seasons. But average gets a slight edge. See below.

NOAA predicts 12 to 17 named storms (winds of 39 mph or higher). Of those, 5 to 9 could become hurricanes (winds of 74 mph or higher), including 1 to 4 major hurricanes (category 3, 4 or 5; with winds of 111 mph or higher). NOAA has a 70% confidence in these ranges.

2023 Hurricane Season Names

Below is a list of storm names for this hurricane season.

Source: National Hurricane Center

Competing Factors Make Forecast Difficult

Competing factors both suppress and encourage storm formation.

After three hurricane seasons with La Nina present, NOAA scientists predict a high potential for El Niño to develop this summer. It can suppress Atlantic hurricane activity.

El Niño’s strong winds from the west produce sheer that can discourage tropical storms approaching from the east.

However, favorable conditions include:

  • Above-normal west African monsoon formation that produces some of the stronger and longer-lived Atlantic storms
  • Warmer-than-normal sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea which creates more energy to fuel storm development.
Updated May 29, 2023. For more information, see this page on methodology.

The last two factors have produced more active Atlantic hurricane seasons since 1995, according to NOAA.

New Policies, Models, Technologies Will Improve Future Forecasts

To improve forecasts, NOAA is adopting new policies, forecasting models and technologies this year. Improvements include:

  • In late June, the Hurricane Analysis and Forecast System (HAFS) will become operational. HAFS will become NOAA’s primary hurricane model. Compared to previous models, it improves track forecasts 10-15%.
  • A Probabilistic Storm Surge model upgrade gives forecasters the ability to run the model for two storms simultaneously.
  • The National Hurricane Center’s Tropical Weather Outlook graphics will expand the forecast range from five to seven days.
  • Over the last 10 years, flooding from tropical rainfall was the single deadliest hazard. To give communities more time to prepare, the Weather Prediction Center is also extending the Excessive Rainfall Outlook two days. It will now provide forecasts up to five days in advance. The outlook shows general areas at risk for flash flooding due to excessive rainfall.
  • The National Weather Service will unveil a new generation of forecast flood inundation mapping for portions of Texas in September 2023. These maps will show the extent of flooding at the street level.
  • New small aircraft drone systems, the deployment of additional saildrones, underwater gliders, and WindBorne global sounding balloons will fill critical data gaps and improve hurricane forecast accuracy.
  • Upgrades to the Tropical Atmosphere Ocean buoy array will provide new capabilities, updated instruments, more strategic placement of buoys, and more detailed observations.

NOAA emphasizes that its hurricane forecast is not a landfall forecast. Many storms die at sea and never reach land.

Peak of Season Still Three Months Away, But…

The Climate Prediction Center will update the 2023 Atlantic seasonal outlook in early August, just prior to the historical peak of the season.

peak of hurricane season

Historically, the peak of hurricane season hits on September 10. However, storms can develop any time of year. Interestingly, NHC determined that a subtropical storm formed in the Atlantic Basin in Mid-January 2023.

And minutes after I first posted this story, the National Hurricane Center issued this 7-day outlook. It shows a disorganized area of showers and thunderstorms over the central Gulf of Mexico trying to get organized. But the chances of tropical formation are slim: 10% in the next two days and 20% in the next seven.

So remain alert and prepared.

Posted by Bob Rehak on 5/30/2023

2100 Days since Hurricane Harvey


Hurricane Hunter Expo at Ellington Draws Crowd

To kick off National Hurricane Preparedness week, the U.S. government sent two hurricane hunter aircraft to Ellington Field today. It was a rare opportunity for the public to interact with crews and support staff, and to tour some impressive displays of technology. See pics below.

Hurricane Hunter Aircraft on Display at Ellington Field

WP-3D – “Orion” by Lockheed. Introduced in 1976. the W stands for Weather. Operated by 53rd Weather Reconnaissance Squadron of the U.S. Air Force Reserves.

The versatile WP-3D – “Orion” turboprop aircraft is equipped with a variety of scientific instruments, radars, and recording systems for both in-situ and remote sensing measurements of the atmosphere, the earth, and its environment. Orion aircraft collects low-altitude data to fill gaps in data not available from ground-based radar or satellite imagery.

A crew member described the aircraft as a flying MRI machine that can see into the heart of storms.

WC-130J – “Hercules”, also by Lockheed is larger and heavier.

The WC-130J is a high-wing, medium-range aircraft used in several weather reconnaissance missions throughout the year. The Air Force configured this plane to penetrate tropical disturbances and storms, hurricanes and winter storms. It is equipped with meteorological instruments and radar to obtain data on the current development, movement, size and intensity of these systems.

The aircraft carries a minimum crew of five: pilot, co-pilot, navigator, aerial reconnaissance weather officer and weather reconnaissance loadmaster. The crew collects and reports weather data as often as every minute.

Members of the public look at the impressive number of missions this hurricane hunter has flown.

Dropsonde Demo

Tube through which instrument sensors called “sondes” are dropped from WC130 into hurricanes.

In flight, the aircraft drops sondes about every 15 minutes, according to one manufacturer. “Dropsondes play a very important role in the data collection during field projects. They provide data of a near-vertical profile of very remote regions that could otherwise not be be studied. The dropsonde provides actual readings of the atmosphere as it travels downward. Because the device is in contact with the medium that it is measuring, this type of sensing is also called in-situ sensing.” They measure temperature, wind speed, wind direction, moisture, location, atmospheric pressure and more.

Emergency Management Participants

Also present were representatives from NOAA, the National Hurricane Center, the National Weather Service, the Army Corps of Engineers, the Coast Guard, the US Air Force, Harris County Flood Control District, the City of Houston Mayor’s Office of Emergency Management, the Red Cross, USAA, and more.

They passed out everything from disaster preparedness guides to hurricane guides, emergency document bags, cloud charts, and stress balls! Good times and sunburns were had by all!

Additional Preparedness Resources

From Houston, the tour moves east to New Orleans, and Mississippi before making two stops in Florida.

In addition to the list of preparedness links I posted yesterday, the handouts today reminded me that I should have posted:

The last guide goes beyond hurricanes and covers everything from chemical spills to active shooter incidents.

They’re all worth exploring. But don’t wait until a hurricane is bearing down to explore them. The sites will likely be crowded, the internet down, and response times slow. Also keep in mind that in an emergency, you may need to conserve battery power in your mobile devices. After Hurricane Ike in 2008, parts of the Lake Houston Area lost power for weeks.

Posted by Bob Rehak on 5/1/2023

2071 Days since Hurricane Harvey

Mark Your Calendar: Tour Hurricane Hunter Aircraft on May 1

NOAA, the National Weather Service and the Hurricane Hunters will sponsor a public tour of Hurricane Hunter aircraft at Ellington Field on Monday, May 1, 2023. It’s all part of a Hurricane Awareness Tour open to the public.

Hurricane Hunter
What You Can Do:

Tour the NOAA-P3 and the USAF C130 Hurricane Hunter aircraft. Mingle with the pilots and air crews. Meet experts from the National Weather Service and National Hurricane Center, including the newly appointed NHC Director Michael Brennan.

There will be numerous static displays including other aircraft and disaster response vehicles. The US Coast Guard will display a helicopter and flood boat.

Representatives from various agencies will pass out hurricane preparedness materials.

  • Speak with hurricane forecasters
  • Meet with local National Weather Service meteorologists
  • Walk through exhibits from various agencies & organizations
  • Learn about weather safety & preparedness
List of Booths:
  • Nws Houston/Galveston
  • Harris County Office Of Homeland Security And Emergency Management
  • Harris County Flood Control District
  • City Of Houston Office Of Emergency Management
  • United States Army Corps Of Engineers
  • USAA – United Services Automobile Association 
  • Flash – Federal Alliance For Safe Homes
  • American Red Cross
Where:

Ellington Airport, near Hangar G

11210 Blume Ave

Houston, TX 77034

See this PDF for directions.

When:

Public viewing period from 12:30 pm to 4 pm. 

Gates close to entry at 3 pm. 

Plan on about an hour to view the aircraft and displays.

Free And Open to All:

There is no charge to tour the Hurricane Hunters. This event is free and open to all as part of National Hurricane Preparedness Week, April 30-May 6.

For more details and directions, click here.

And remember, hurricane season is just weeks away.

Posted by Bob Rehak on 4/18/2023

2058 Days since Hurricane Harvey

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