Tag Archive for: storm surge

Tsunamis, Storm Surge Demonstrate Power of Moving Water

12/5/2024 – Tsunamis are huge waves caused by earthquakes. Storm surge is a huge wave caused by hurricane winds. Both have unimaginable destructive power.

Bolivar after Ike
Destruction on Bolivar Peninsula from Hurricane Ike storm surge in 2008.

West Coast Tsunami Warning This Morning

This morning, a magnitude 7.3 earthquake struck Northern California. That caused the National Weather Service to issue tsunami warnings from Oregon down to San Francisco and beyond.

About three hours later, the warning was cancelled without explanation. Since then, significant aftershocks ranging from 3.0 to 5.3 magnitude have occurred. We will learn more in coming days.

From EarthquakeTracker.com

Different Types of Earthquakes Trigger Different Tsunami Threat Levels

Massive earthquakes don’t always trigger massive tsunamis. The magnitude 7.9 quake that destroyed much of San Francisco in 1906 reportedly produced a wave height of only three inches. Small localized, underwater landslides created 1-2 foot waves, but their destruction was confined to small areas.

Geology determines, in large part, the height of a tsunami. Imagine two different types of geologic faults.

In a thrust fault, one tectonic plate is forced under another, pushing it up and causing a vertical displacement of the seafloor. This type of fault commonly generates a tsunami.

However, a strike-slip fault causes a lateral displacement. Land along a fault moves in opposite directions without causing elevation changes. Strike-slip faults typically do not generate tsunamis because they generally do not displace large volumes of water. (Contrast the animations in the two links above.)

Other factors may also affect tsunami formation. They include:

  • Depth: Shallow earthquakes (occurring at depths less than 70 km) are more likely to cause tsunamis than deep earthquakes, as the energy has a more direct impact on the seafloor.
  • Seafloor Topography: The configuration of the ocean floor, including ridges and trenches, can amplify or reduce tsunami formation.
  • Underwater Landslides or Underwater Volcanic Activity triggered by the earthquake can also contribute to tsunami generation.

In summary, while massive offshore earthquakes increase the risk of tsunamis, they do not guarantee one will occur.

In this case, officials issued the tsunami warning out of an abundance of caution when seismographs first detected the earthquake. Later, they cancelled the warning when it became clear no massive waves threatened. They made the right call initially. Here’s why.

Record Waves, Record Destruction

Some massive earthquakes, like the magnitude 9.0, 2011 Tōhoku earthquake in Japan, did produce devastating tsunamis. One wave reached more than six miles inland. A 48-foot high tsunami wiped out a nuclear power plant at Fukushima. And the death toll ultimately reached almost 20,000 people.

So you can imagine why California officials immediately issued warnings today for residents to evacuate to higher ground.

During the great Galveston hurricane of 1900, a giant wave of water caused by storm surge, not a tsunami, inundated the island with 8- to 12-feet of water. It killed an estimated 6,000 to 12,000 people.

One cubic foot of seawater weighs 64 pounds. Imagine getting stuck by tens of thousands of cubic feet. That’s why storm surge is the leading cause of death associated with tropical events, according to the National Weather Service.

Don’t take either storm surge or tsunamis lightly.

Elevation: Key to Survival

The National Weather Service’s Tsunami Warning Center offers an excellent FAQ page concerning tsunami warnings.

Interestingly, shortly after NWS issued the tsunami warning for the San Francisco area this afternoon, I had a huge spike in traffic on ReduceFlooding.com. Everyone was going to a post with the headline “Easy way to find the elevation of your home and the slopes around it.

I notice the same spike in traffic every time floods threaten. People want to know whether they live higher than the expected crest of the flood, storm surge or, in this case, tsunami.

Published in 2020, the post has received more than 150,000 page views already this year. The biggest peaks were during the May storm, Beryl, Helene and Milton.

Ironically, when I wrote that post about elevation, tsunamis were the furthest thing from my mind.

Even more ironic, shortly before the warning, someone emailed me asking whether I thought a development near the San Jacinto West Fork was safe from flooding. I replied to her that if she had a concern about flood risk, she should buy on the highest ground she could afford, as far from the water as she could get.

Posted by Bob Rehak on 12/5/2024

2655 Days since Hurricane Harvey

Laura Upgraded to Hurricane; Will Intensify Through Landfall; Mandatory Evacuation for Galveston Island

Overnight, Laura turned into a hurricane. At 5:25 this morning, Jeff Lindner, Harris County Meteorologist, issued the following:

Hurricane Watches extended west to San Luis Pass…now include Harris and Galveston Counties

Major hurricane forecast in the NW Gulf of Mexico Wednesday

Enact hurricane plans now. Follow all recommendations from local officials.

At 7:00 a.m., he issued another warning saying that:

Laura upgraded to a hurricane…intensification will continue through landfall.

Mandatory evacuation order for Galveston Island effective immediately.

Discussion 

Laura is now over the SE Gulf of Mexico and moving toward the WNW after having jogged westward overnight. Deep convection has developed over and near the center this morning. Some light northerly system continues to impact Laura, which continues to track to the south of predictions. 

Track: 

The steering pattern that will bring Laura to the NW Gulf of Mexico remains somewhat in flux this morning. Laura will turn northwest and then north. But uncertainty remains as to when Laura will make this turn. Overnight model guidance now delays this turn a little longer and brings Laura more toward the upper Texas coast. NHC may have to shift their forecast track a bit more westward later this morning.

Forecast track shifted back west overnight bringing Houston into cone of uncertainty. Track forecast could shift further westward later this morning, bringing Houston closer to center of storm.

While uncertainty remains in the eventual outcome of Laura, preparations for landfall of a major hurricane along the upper TX coast should be well underway.

Jeff Lindner, Harris County Meteorologist

Tropical storm force winds will begin to arrive along the coast Wednesday evening and spread inland Wednesday night into Thursday morning.

Intensity: 

A central core is starting to form with Laura and overall circulation of the system is looking better defined. Conditions in the central Gulf today favor a period of rapid intensification. Laura is forecast to make landfall as a major hurricane along the SE TX/SW LA coast late Wednesday.

Laura is a fairly large storm and impacts will be far reaching from the impact point extending both west and east.

Tropical-storm-force winds currently extend outward up to 175 miles (280 km) from the center.

Impacts

Rainfall:

Will rainfall forecast at 2-4 inches east of I-45 and 1-3 inches west of I-45, but this may need to be increased later today. WPC has placed areas east of I-45 in a slight risk for flash flooding.

Most of Houston falls into the light and dark green bands on the left, predicted to get 1-4 inches of rain.
NHC how gives the Houston Area a slight chance of flash flooding (10-20%).
Storm Surge: 

Still looking at 2-4 feet above ground level in Galveston Bay and 4-6 feet on Bolivar with levels of 7-11 feet east of High Island into Louisiana. Should the track shift more west, these values around Galveston Bay would potentially need to be increased significantly.  

Wind: 

Tropical storm force winds will be moving into the area Wednesday evening. Expect winds of 40-50mph across Harris County northward along I-45 with hurricane conditions becoming increasingly likely over Liberty and Chambers Counties. Any additional shift westward in the track will bring stronger winds across the area.

Be prepared for power outages starting Wednesday evening. 

Actions

Enact hurricane plans now.

Follow all recommendation on evacuation from local officials.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT

The National Hurricane Center advises that:

Storm Surge Watch is in effect for San Luis Pass Texas to Ocean Springs Mississippi.

  • High Island TX to Morgan City LA including Sabine Lake, Calcasieu Lake, and Vermilion Bay…7-11 ft
  • Port Bolivar TX to High Island TX…4-6 ft
  • San Luis Pass TX to Port Bolivar TX…2-4 ft
  • Galveston Bay…2-4 ft

Hurricane Watch is in effect for San Luis Pass Texas to west of Morgan City Louisiana

Tropical Storm Watch is in effect for…

  • San Luis Pass to Freeport Texas
  • Morgan City Louisiana to the Mouth of the Mississippi River

A Storm Surge Watch means there is a possibility of life-threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours.

A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous.

For inland watches and warnings, monitor the local National Weather Service forecast office.

Posted by Bob Rehak on 8/25/2020 with input from CoH, Harris County, National Hurricane Center, National Weather Service, and ReadyHarris.

1092 Days After Hurricane Harvey

NHC Says Marco Now Hurricane, Laura Shifting West

As of 2 p.m. Sunday, Tropical Storm Marco has officially turned into a hurricane and the National Hurricane Center (NHC) shows Laura continuing to shift toward the west.

Current positions of both storms as of 1:19 EDT Sunday, 8/23/2020.

NHC Forecast for Marco as of 1pm CDT

At this time, Marco is not a large threat to the Houston Area. However storm-surge warnings are up from Sabine Pass to Mobile Bay. Parts of coastal Louisiana could receive 4-6 feet of life-threatening storm surge.

The heaviest rain from Marco should hit from Louisiana to the Florida Panhandle.

NOAA no longer predicts even a marginal risk of flash flooding from Marco for the Houston Area.

However, Houston could still feel significant wind from Marco. NHC shows Houston has a 60-70% chance of feeling tropical-storm-force winds (40 mph or higher).

The most likely arrival time for the winds will be Tuesday morning.

After Marco comes ashore as a hurricane, it will rapidly diminish to a tropical storm and then a tropical depression. NHC currently shows the remnants of the storm curling back into north Texas by next Tuesday or Wednesday.

Space City Weather predicts, “Most of the winds and heavy rainfall should remain to the east and north of the center, we do not anticipate severe conditions in the Houston region from Marco.”

Laura May Now Be Larger Threat to Houston Area

Overnight the cone of uncertainty for Tropical Storm Laura shifted west toward east Texas. The most likely track is currently right up the Texas/Louisiana Border. Laura is currently a tropical storm, projected to intensify into a hurricane on Tuesday and Wednesday as it approaches the central Gulf coast.

NOAA predicts Laura could dump 4-6 inches of rain on the Houston Area.

As with Marco, NHC predicts a 60-70% chance of tropical-storm-force winds for the Houston Area.

The most likely arrival time for Laura’s winds in the Houston Area will be Wednesday evening.

Net: Laura could result in a prolonged period of hazardous weather for areas likely to be affected by Marco earlier in the week.

Uncertainty Remains So Continue to Monitor Forecasts

Considerable uncertainty remains about both storms. Models disagree over where Laura will make landfall. They range from Corpus Christi to New Orleans at the moment. Space City Weather points out that “For the National Hurricane Center, the average track position error at 3.5 days before landfall is about 120 miles, which is a little bit greater than the distance between downtown Houston and the Texas-Louisiana border on Interstate 10.”

So what should you do? Continue to monitor the progress of both storms throughout the week at Hurricanes.gov or on your favorite weather channel.

Posted by Bob Rehak on 8/23/2020 based on input from Space City Weather, the National Hurricane Center, and Jeff Lindner, Harris County Meteorologist.

1090 Days after Hurricane Harvey