25 August 2017

Harvey nearly a major hurricane as it heads for Texas landfall tonight

At 8am EDT on Friday, the National Hurricane Center upgraded Hurricane Harvey to a Category 2 storm with peak winds of 110 mph. It is the third hurricane of the season and is extremely close to becoming the first major hurricane of the season (115mph+).  Landfall is forecast to be near Corpus Christi late Friday night into the early morning hours on Saturday.

Impacts on Texas have already begun and conditions will deteriorate throughout the day.  The central pressure as of 8am EDT is 950 mb and still falling - Harvey's dramatic intensification has not slowed down yet.  The eye is about 140 miles from Corpus Christi, but rainbands are already affecting the Texas coast, and tropical storm force winds will arrive by later in the morning.

The impacts from this storm are anticipated to be almost unfathomable.  A storm of this intensity would be bad enough, but all guidance suggests that it will stall for several days right near the coast due to a lack of mid-level steering winds.  The rainfall forecasts are ominous, and if they come even close to verifying, this will be a storm for the history books. In this map below, which shows the cumulative rainfall forecast over the coming week, a large area is saturated at the >20 inches contour, but specific locations could see 3-4 FEET of rain.  Widespread and prolonged life-threatening flooding appears inevitable.

In addition, the storm surge will be significant near the landfall location and for hundreds of miles to the right/east.  This impact will be exaggerated around the times of the normal astronomical high tides, but areas near the landfall point could see inundation levels of 6-12 feet.

As I said for an Associated Press interview yesterday, "Harvey combines the worst attributes of nasty recent Texas storms: The devastating storm surge of Category 2 Hurricane Ike in 2008; the winds of Category 4 Hurricane Bret in 1999 and days upon days of heavy rain of Tropical Storm Allison in 2001."

I have a series of long, updating radar loops to cover Harvey at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/, and as of this writing (8am EDT), this is the view from the Corpus Christi radar:

For the latest information and updates on storm intensity, watches, warnings, forecasts, etc, consult the National Hurricane Center.  You can also follow frequent updates on the Capital Weather Gang blog.

The last hurricane to make landfall on Texas was Ike in 2008 (9 years ago), and the last major hurricane to make landfall on Texas was Bret in 1999 (18 years ago).

If Harvey strengthens just slightly by landfall, it will be the first major hurricane to make landfall on the United States since Wilma in 2005, a record-smashing 4323 days ago.  A major hurricane is defined to be one that is a Category 3 or higher on the Saffir-Simpson scale (115mph+ sustained winds). This "major hurricane drought" has largely been due to pure luck.  Other countries have been hit by major hurricanes since then, and the U.S. has had some close calls.

Since Wilma, the U.S. has been hit by ten hurricanes, all Category 1 and 2 storms... though some were certainly still significant and destructive.  The list includes:
Humberto 2007
Dolly 2008
Gustav 2008
Ike 2008
Irene 2011
Isaac 2012
Sandy 2012 (not technically a hurricane at landfall)
Arthur 2014
Hermine 2016
Matthew 2016

A key message here is that it does not take a major hurricane to cause a tremendous amount of damage.  Storm surge and rainfall are big players even in weaker storms, but major hurricanes add extremely strong winds to the mix. "There's more to the story than the category".

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