Thursday, August 24, 2017

Hurricane Warning: "Dangerous, Rapidly Intensifying Harvey Expected to be a Major Hurricane"

Following up on Tuesday's "Hurricane Watch: 'Atlantic tropical activity forecast above-average over next two weeks'".
As the kids might say, "Well that intensified quickly".

This could be a disaster in the making, Some of the analogs being mentioned are 1970's Hurricane Celia for storm track:

Celia may be a model for intensification as well, ramping up from a tropical depression with 35 mph winds on Aug. 1 to a category 3 hurricane with 125 mph winds on August 3, 1970.

Another comparison being made is tropical cyclone rainfall. The current U.S. single-event record is 1978's  Tropical Storm Amelia which dumped 48 inches (1,200 mm) on Medina Texas. The next year's Tropical Storm Claudette set the U.S. (and Texas, natch) 24-hour record of 42 inches (1,100 mm) at Alvin TX.

This morning we saw at least one usually reliable source comment that should Hurricane Harvey both turn north up the Texas coast rather than head directly inland and slow its forward momentum Hurricane Flora might be analogous.
That would be very, very bad.
1963's Flora poured 100.39 inches (2,550 mm) of rain on Santiago De Cuba.

Anyhoo, enough history here's Wunderground's Category 6 (né WunderBlog before IBM bought 'em):
Hurricane Warnings and Storm Surge Warnings are up for portions of the coast of Texas as rapidly intensifying Tropical Storm Harvey heads north-northwest at 10 mph over the Gulf of Mexico. Harvey was still a tropical depression at 10 pm CDT Wednesday night, but has explosively intensified in the early morning hours, and is almost certain to be a hurricane later today. Update: The National Hurricane Center (NHC) has upgraded Harvey to a Category 1 hurricane with 80-mph sustained winds as of noon CDT Thursday. If you live on the coast of Texas, please heed the advice of local emergency management officials, and get out today if you live in an evacuation zone. Tropical storm-force winds may arrive along the coast of Texas as early as 8 am CDT Friday, making evacuation difficult thereafter, according to the latest National Hurricane Center (NHC) forecast. 
Harvey rapidly strengthening
At 6:42 am CDT Thursday, an Air Force hurricane hunter plane found that Harvey had formed a partial eyewall, with a 986 mb pressure. By 8:04 am CDT, the eye had completely closed off, and the pressure had fallen another 2 mb, to 984 mb. By 10 am CDT, the pressure had fallen another 2 mb, to 982 mb. This is the central pressure that a Category 1 hurricane typically has, but the Hurricane Hunters measured top surface winds of just 65 mph. It takes up to six hours for a tropical cyclone's winds to respond to a fall in pressure, so I expect that Harvey will be a hurricane by the 4 pm CDT Thursday advisory.

Conditions in the Gulf of Mexico on Thursday morning were very favorable for intensification. Satellite images showed that Harvey was a large storm, whose high-level cirrus clouds were already spreading over extreme southern Texas. Harvey had an intense ring of heavy thunderstorms surrounding the eye, and solid low-level spiral bands were forming. The eye was just beginning to appear on both visible and infrared imagery at 10 am CDT. High cirrus clouds streaming away from the center showed the presence of upper-level outflow to the north and east, which was ventilating the storm and allowing intensification to occur. Wind shear was light, 5 – 10 knots, which is favorable for intensification. The atmosphere had a high mid-level relative humidity of 70%, and the ocean was very warm, with sea surface temperatures (SSTs) of 30.5°C (87°F.)  This was about 2°F above average for this time of year. Warm waters extended deep into the ocean, providing a large reservoir of heat for the storm to draw upon. The outer bands of Harvey are visible on Brownsville long-range radar....
Harvey intensity forecast 
Figure 4. Intensity forecasts made for Harvey at 2 am EDT Thursday, August 24, 2017. Most of the reliable intensity models predicted Harvey would be a Category 2 or 3 hurricane by landfall on Friday night on the coast of Texas. 
Image credit: Image credit: NOAA/NCEP/EMC.


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