Hurricane Harvey slams ashore in Texas, catastrophic flood threat still to come – “An area larger than the state of Massachusetts, including Houston and Galveston, can expect more than 20 inches of rain between now and Wednesday”

Desdemona Despair

By Bob Henson
26 August 2017

(Weather Underground) – Hurricane Harvey ripped into the central Texas coast as a Category 4 storm late Friday night. Harvey’s center made landfall just before 10 pm CDT about 4 miles east of Rockport with top sustained winds estimated by the National Hurricane Center (NHC) at 130 mph, which is minimal Category 4 strength. A parachute-borne dropsonde instrument package deposited by a Hurricane Hunter flight around 10 pm found that Harvey’s pressure had dropped to 938 millibars. Since the surface winds at this point were 10 knots, the dropsonde did not sample the true center of the storm, so the actual central pressure is probably a millibar or so lower. Microwave measurements from the aircraft estimated that surface winds were 111 knots (128 mph).

Harvey is the first Category 4 storm to strike the U.S. since Hurricane Charley in 2004, and the first major hurricane (defined as Category 3 or stronger at landfall) since Hurricane Wilma in 2005. Several more recent hurricanes that reached land without Category 3 winds were still large and powerful enough to deliver a devastating storm surge, including Ike (2008) and Sandy (2012). […]

As of late Friday night, there was no major change to the prognosis for extreme rainfall and potentially devastating flooding from Harvey from this weekend through at least part of next week. Harvey’s core and its eye remained impressively well structured even as it moved almost completely onshore late Friday night, and the hurricane may take longer than usual to spin down given its expected proximity to the coast. The 10 pm CDT forecast from NHC slows Harvey to a crawl on Saturday, still at hurricane strength, then keeps the storm within about 100 miles of its landfall location as a tropical storm from Sunday until Wednesday, when it is predicted to creep toward Houston. Because steering currents will be so weak and difficult to analyze over the next several days, various models have different tracks for Harvey within Texas, but they generally agree any motion will be very slow to occur.

The latest 5-day precipitation outlook from the NOAA/NWS Weather Prediction Center (see Figure 3) projects that an area larger than the state of Massachusetts, including Houston and Galveston, can expect more than 20” of rain between now and Wednesday. Amounts of more than 10” cover an even larger area, extending into parts of the Austin-San Antonio urban corridor and including Corpus Christi and Beaumont-Port Arthur, TX, and Lake Charles, LA. Local rainfall amounts could be far above 20″, as suggested by multiple models. Very serious flooding over the next several days can be expected well inland from the areas immediately at risk from Harvey’s initial landfall and storm surge. For example, Austin/San Antonio NWS office notes the potential for life-threatening flash flooding, especially from San Antonio south and east.

There is virtually no precedent for such a slow-moving system maintaining at least tropical storm strength along the Texas coast for five days. [more]

Harvey Slams Ashore in Texas; Catastrophic Flood Threat Still to Come