It's rare to have a Category 4 or higher hurricane make landfall in the United States.
Counting Harvey, it's only happened three times in the last 37 years. The other two were Category 4 Charley in 2004, and Category 5 Andrew in 1992.
Both of those hurricanes hit Florida.
The circumstances, the variables and the meteorology that all had to come together with just the right timing to create this historic weather event is astonishing.
The first element of Harvey’s creation, or recreation, was the drop in wind shear. Upper level crosswinds are often present in the Gulf of Mexico and can prevent hurricane formation.
Harvey was originally destroyed by high wind shear in the Caribbean, but the remnants of the storm entered the Bay of Campeche just as the wind shear vanished. The winds became ideal for development.
Then the storm moved over a heat eddy in an already warm Gulf of Mexico. These eddies are always on the move and fluctuating, but Harvey hit one at just the right time as it was redeveloping.
Dr. Kate Musgrave monitors hurricane activity from Colorado State University at the Cooperative Institute for Research in the Atmosphere. She says the new GOES 16 weather satellite that was built here in Littleton has been putting out high detailed data.
It's resolution that we have never seen during a hurricane before.
Musgrave was able to clearly recognize the developing tropical system was going to cross into a heat eddy in an already warm Gulf of Mexico shortly before reaching the Texas coast. These eddies are pockets of very high ocean heat content that are constantly moving and fluctuating. She said the path it took through that eddy may have been the only point that Texas caught a break.
“There was a concern that if it had actually shifted further to the right, it would have been over that even longer,” Musgrave said.
That is just how easily Harvey could have been a Category 5. It was in that heat loop long enough though for some rapid intensification. Harvey went from a tropical storm to a Category 4 hurricane in just 17 hours.
It may be more of a coincidence that the cyclone powered up to its most intense phase just as it made landfall, but the timing was an incredible bad break for those in its path.
Rapid intensification is a tough aspect of tropical forecasting, but it is one of the reasons for Musgrave's dedication to research. She and her team at CIRA will reanalyze the data gathered during Harvey to learn more about rapid intensification. They hope to learn why some storms get a surge in intensity, while other storms in similar conditions do not.
“It’s actually a major concern for the National Hurricane Center. It’s one of their top priorities for research,” said Musgrave.
The final ingredient to this perfect storm was the stall. A ridge of high pressure built in to the north of Texas, just as Harvey was making the slow, short journey onto land.
Harvey was pinned with nowhere to go. The storm sat there, spinning and pulling in storm bands from the Gulf of Mexico. Due to proximity and structure of the storm, most of those bands where focused right over the population center of the east Texas coast, Houston, where record breaking rainfall has devastated the area.
The gauge at Cedar Bayou, Texas measured 51.88 inches of rain during the storm, before it stopped working on the evening of August 29. That makes Harvey the second wettest tropical system to ever hit the United States. The record is held by Hurricane Hiki. It dumped 52 inches of rain, on Kauai, Hawaii, in 1950.