Hurricane Harvey, upgraded to hurricane status today at noon central time, is forecast by the National Hurricane Center to rapidly intensify into a major hurricane that will strike Texas near Matagorda bay then slow to a stall causing catastrophic flooding on the twelfth anniversary of Hurricane Katrina.
Surface wind speeds increased by about 20mph in the time it took for the Air Force hurricane hunter plane to make another pass through the eye of the storm. Winds aloft, shown in the image below, increased even more. After the eye began to form in the mid-morning hours, the central air pressure began to fall rapidly, then the winds began to intensify rapidly.
Harvey is tracking over a deep pool of extremely warm water that extends from the west-central Gulf of Mexico to the Texas coast. With low wind shear and very high ocean heat content, conditions are ripe for rapid intensification of Hurricane Harvey. The NHC’s discussion of Harvey at 10am CDT this morning reminds me of the warnings the NHC issued when Hurricane Katrina exploded off the west coast of Florida under similar circumstances.
Data from an Air Force Hurricane Hunter aircraft indicate that Harvey is quickly strengthening, and the cyclone's structure has improved markedly with the plane reporting a closed 15-20 n mi wide eye. The flight-level and SFMR winds support an intensity of 55 kt,but one of the more notable measurements is the central pressure, which has fallen to 982 mb. With a pressure this low, it is likely that the winds will respond and increase further, and Harvey probably isn't too far from becoming a hurricane.
With Harvey now strengthening at a faster rate than indicated in previous advisories, the intensity forecast has become quite concerning. Water vapor images indicate that the cyclone's outflow is expanding--indicative of low shear--and Harvey will be moving over a warm eddy of high oceanic heat content in the western Gulf of Mexico in about 24 hours. As a result of these conditions, several intensity models, including the ICON intensity consensus, are now explicit showing Harvey reaching major hurricane intensity. What's more astounding is that some of the SHIPS Rapid Intensification indices are incredibly high. As an example, the guidance is indicating a 70 percent chance of Harvey's winds increasing by 45 kt over the next 36 hours. Based on this guidance, the NHC official intensity forecast now calls for Harvey to reach major hurricane strength by 36 hours, before it reaches the middle Texas coast.
Water temperatures on the forecast track range from 86ºF to 88ºF (30C to 31C) and the water is very warm to a depth of greater than 200 feet (75m or more). This kind of oceanic heat is capable of supporting strong category 5 hurricanes. The main thing holding Harvey back is the limited time it will stay over water.
After Hurricane Harvey comes ashore the warm waters will continue to fuel heavy rains for days as Harvey lingers near the coast. Extreme, destructive flooding is likely. Fifteen to twenty inches of rain is forecast by the NWS to fall over a large area of coastal Texas.
See Jen’s DK post about the situation at FEMA www.dailykos.com/…
See JRooth’s excellent earlier post about the storm threat to SE Texas . www.dailykos.com/...
See Darksyde’s FP post on Harvey. www.dailykos.com/...