Article - July 17, 2022

Lessons Learned: Hurricane Harvey

Hurricane Harvey

Preparing for the Future by Understanding the Past

Even if your organization wasn't directly impacted by a specific hurricane, there are still lessons to be learned. By understanding the past, we can become better equipped to understand the future.

Read the Lessons Learned from Barry, Harvey, Ida, Irma and Laura.

One record-breaking storm to impact the United States is Hurricane Harvey, which made landfall north of Corpus Christi, Texas on August 25, 2017 and brought 60+ inches of rain to areas along the upper Texas coast.

Harvey Rainfall

Slow-moving Storms Bring Heavy Rains

Harvey is a good example of a slow-moving powerful hurricane storm causing heavy rainfall and tremendous flooding.

Tropical storms are steered by global winds, like trade winds and westerlies. Within these winds, high-pressure and low-pressure systems influence the direction a storm will take, as winds tend to move from high- to low-pressure systems. As a storm is moved inland, it loses access to its warm-water fuel and dissipates.

As it moved inland, Harvey was caught in a weak frontal boundary between two high-pressure systems stalling its northward movement. Because the system stalled close to the coast, it was able to continue to draw moisture from the Gulf, bringing more rainfall inland, even as its wind speeds dropped tropical storm levels.

Meteorologists can predict whether a storm will stall and have the potential for heavy rains. The difficulty is predicting exactly what area is going to have the most rainfall when a hurricane, or even a tropical depression or tropical storm, is making landfall. Rainfall amounts are not influenced by the intensity of the storm but by the storm’s speed of movement.

Lesson to be Learned

The amount of rainfall that accompanies a storm does not correlate to wind speeds but is determined by how slowly a storm moves over an area. Two storms to cause the most flood damage to the Houston areas were Hurricane Harvey and 2001’s Tropical Storm Alison, both storms had tropical-storm-rated wind speeds in the areas with the highest rainfall.

To prepare your business for high volumes of rain, it is important not to downplay the potential damage that can accompany a tropical storm or category 1 hurricane. Make sure your hurricane response plan includes actions to take in the event of forecasted heavy rains. This includes moving sensitive equipment out of the range of potential flooding and monitoring roadways for potential blockages due to flooding.

Hurricane Harvey Events Timeline

StormGeo monitored the development of Hurricane Harvey closely, continuing to issue alerts after the storm was downgraded after passing the Yucatan and bringing attention to the potential for widespread flooding.

August 11th

A strong tropical wave moving off the west coast of Africa was identified and given the designation Tropical Disturbance 30. The wave was monitored daily in the Atlantic Daily Briefing.

August 17th

StormGeo issued its first storm-specific advisory for Disturbance 30 at 10 AM. The National Hurricane Center designated the disturbance a Potential Tropical Cyclone a few hours later. By afternoon, Harvey had been upgraded to a tropical storm. While the extended forecast had low certainty, these initial advisories did mention the possibility that the system would dissipate over Mexico but could intensify quickly as it emerged into the Bay of Campeche.

August 19th

After causing damage across Barbados and St. Vincent the previous evening, as Harvey moved into the Caribbean, the hostile environment caused the system to degenerate to an open tropical wave. At this point, the National Hurricane Center stopped issuing advisories for this system, resulting in a gap from August 19th at 10 PM through August 23rd at 10 AM. As system regeneration seemed likely, StormGeo continued issuing advisories every 6 hours to keep clients informed of Harvey’s status.

August 21st

As the system reached the Yucatan Peninsula, StormGeo meteorologists began to highlight the increasing threat of flooding rain potentially affecting areas from Northwest Mexico to as far north as Houston, TX.

August 23rd

Harvey was officially reclassified as Tropical Depression Harvey.

August 24th

Harvey completed a rapid intensification cycle, quickly upgrading the storm to an 85-mph hurricane. Both StormGeo and the NHC were forecasting that Harvey would make landfall as a major hurricane along the lower or middle Texas coast, with little motion shown thereafter.

5-day TRAC Model Guidance from 9AM Thursday, August 24th. Note how little the models moved the storm over 5 days.

August 25th

It was becoming readily apparent that a major-landfalling hurricane and extensive flooding event was on tap for southeast Texas. Advisories at the time were forecasting rainfall totals of more than 20 inches with discussions indicating that some models were forecasting upwards of 4 feet of rain. This is an incredibly high forecast total but ended up being on half the amount of rainfall measured. Overnight, Harvey made landfall near Rockport, TX as a Category 4 hurricane, with winds of 130 mph and a Hurricane Severity Index (HSI) of 25.

Harvey Rain Forecast

August 26th

As Harvey made landfall, the system quickly weakened down to a tropical storm. StormGeo Forecasters shifted focus to determining the areas along southeast Texas that would receive the worse flooding impacts. Heavy rain bands moved eastward across southeast Texas through the day and into the Houston area overnight, causing extensive flooding with some areas of Harris County receiving as much as 17-22 inches of rain in a 12-hour period.

August 27th – 29th

Additional heavy bands of rain and thunderstorms continued to develop and move across the Houston area helping to pile up extreme amounts of rainfall, as round after round of heavy weather inundated much of the region. During this period through August 29th rainfall totals reached totals approaching 50 inches in Harris County and extended into the Beaumont, TX area and southwest Louisiana.

August 30th

By this point, rainfall had largely come to an end for the Houston area, although flooding impacts were continuing to be felt as water levels continued to rise. To prevent a catastrophic failure of the reservoir system, the Army Corps of Engineers was forced to release water causing extensive additional flooding that lasted well into the following week. Harvey continued to move across central Louisiana throughout the day, continuing to produce locally heavy rainfall across portions of the Lower Mississippi River Valley and across western and central Tennessee and Kentucky through September 1. StormGeo issued the final advisory for Harvey on August 31st at 7 AM.

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