Tom Konvicka's Hurricane Harvey Outlook
Chief Meteorologist Tom Konvicka shares his thoughts in this Thursday evening outlook.
HURRICANE HARVEY POISED TO ACHIEVE HISTORICAL RECOGNITION. Harvey is spinning in the western Gulf of Mexico about 275 miles southeast of Corpus Christi, Texas. The maximum sustained winds are 85 mph, making Harvey a Category I hurricane. But expectations for Harvey are high. Here are some of my thoughts.
HARVEY'S INTENSITY. Conditions favor strengthening. Sea-surface temps are in the middle 80s (thanks to a warm eddy that recently broke away from the Loop Current) and deep-layer vertical wind shear along the expected track of Harvey to the Texas coast is about 10-15 knots, Some mid-level dry air; however, is halting significant strengthening for now but that is expected to be temporary. Reliable guidance predicts Harvey to be anywhere from a Category I to a Category III strength just prior to landfall. My feeling is Cat. II or III. IF Harvey makes landfall at Category III strength, then it would be the first hurricane to do that in Texas since Bret in 1999 and the first on U.S. soil since Wilma hit Florida in 2005.
HARVEY'S MOVEMENT. The path to landfall is straightforward because Harvey is being steered by high pressure aloft over the eastern Gulf of Mexico. This feature will steer Harvey toward the northwest or north-northwest through the time of landfall. The forecast really gets tricky after landfall as the steering ridge to the east erodes and a larger, stronger ridge builds over the western U.S. This will cause Harvey to slow down and move erratically or very little for about two to three days. As the western ridge builds, the laws of physics dictate that a trough will develop on the east side of the ridge. This trough in the jet stream will phase with Harvey and a generally eastward motion should begin Monday. As the Harvey/trough combo continues to phase, a sustained but slow eastward movement should persist through next week. It's a close call whether Harvey will move back out into the Gulf or stay slightly inland.
HARVEY RAINFALL. This will be Harvey's main legacy if the above scenario pans out. Storm totals, over several days, may reach 20-40 inches near and inland from the middle and upper Texas coast. In the annals of history, Harvey could join Tropical Storm Amelia in 1978 (48 inches), Claudette in 1979 (45 inches), and Allison in 2001 (40.68). In central Louisiana amounts would range from several inches to 15-20 inches. The timing of the heavy rain for central Louisiana would be Sunday through Wednesday.
HARVEY WIND AND TORNADOES. Harvey will bring damaging winds to the Texas coast and perhaps over 100 miles inland. While that is typical for hurricanes, Harvey may also bring a huge number of tornadoes because the slow movement will bring prolonged periods of strong low-level wind shear. Hurricane Beulah triggered 115 tornadoes as a Category III hurricane in 1967. In central Louisiana, at least a low-end risk for tornadoes and strong wind will be present early next week. Should Harvey move back out over the northern Gulf and intensify, the tornado and high wind threat would increase.
As always, let's watch this storm closely!