26 August 2017

Harvey made landfall as Category 4 hurricane, but the disaster is far from over

At about 10pm local time on Friday, Harvey made landfall near Rockport, TX.  It rapidly intensified for two days leading up to landfall, and ended up crossing the coastline with 130 mph winds... a Category 4 hurricane.  It was the strongest hurricane hit the U.S. since Charley in 2004, and the strongest hurricane to hit Texas since Carla in 1961.

Infrared satellite image of Hurricane Harvey at the time of landfall.
Just two days prior to this, Harvey was a tropical depression with 35 mph winds.  Although it was forecast to become a hurricane by landfall, this extreme rate of intensification is unpredictable.  Hurricane watches were issued on Wednesday morning for the appropriate section of coastline... that is the maximum lead time used in tropical cyclone watches.
Hurricane watches were issued for Texas coast on Wednesday morning for a forecast landfall on Friday night.  Harvey was a tropical depression at this point.
As of early Saturday afternoon, Harvey is still a Category 1 hurricane and has already stalled over Texas.  It's extremely important that people in the area do not breathe a sigh of relief now that landfall is behind them.

Regional radar image from midday Saturday.
The big story has been and still is the rain.  This part of the event is just beginning to unfold.  The forecast still calls for Harvey to remain essentially stationary for at least the next five days.  From Friday morning through Saturday morning, rainfall totals are already impressive, especially in areas just north of Corpus Christi.  I have numerous long radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

Observed rainfall totals from midday Friday through midday Saturday.
A stationary tropical cyclone is a very bad thing... and widespread life-threatening flooding is anticipated over the coming days.  The latest 5-day rainfall forecast places over 20 inches of rain in the same areas that have been getting heavy rain since Friday morning. Locations within this area could see up to 40 inches.  Flooding might not be as dramatic as a hurricane making landfall, but it's more deadly.

Cumulative rainfall forecast over the coming five days.
Like most major hurricanes, Harvey originated from Africa.  The easterly wave that went on to become Harvey left the African coast on August 12 and was a trackable feature and/or tropical cyclone the entire time.  Storms like this do not come out of nowhere.

Harvey was also the first major hurricane to hit the United States since Wilma in 2005, so it ended the astounding record span of nearly 12 years between such landfalls.

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