WEATHERAMerica Newsletter UPDATE ON HURRICANE IKE, Wednesday, September 10, 2008

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WEATHERAMerica Newsletter UPDATE ON HURRICANE IKE, Wednesday, September 10, 2008

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Overview

Hurricane Ike is now a Category 2 storm with top winds of 100 mph, situated over the Gulf of Mexico at 24.5 N, 86.5 W or 365 miles south of Venice LA. Central pressure of the hurricane is about 950MB with the tropical storm force winds extending more than 200 miles from the eye.

Next 48 Hours

Hurricane Ike will move over open waters in the Gulf of Mexico beneath a relatively narrow lateral heat ridge straddling the Gulf Coast from Louisiana into northern Florida and southern Georgia. As the circulation of Ike moves closer to the ridge axis, some westward component is inevitable. But with no real shear to speak of and generally warm seas available for warm-core convection, Ike will undergo steady deepening and should be a Category 4 system with winds of 145 mph and core pressures of 925MB by Friday evening, approaching the Texas shoreline.

Final Landfall Point As has been the case with Ike for its entire lifetime, the numerical forecast models have performed poorly while shifting sometimes wildly, particularly with regard to position after 72 hours. The most recent runs of the various outlooks are all clustered over the Texas Gulf Coast from South Padre Island to High Island. Ordinarily, a consensus would favor C TX, and that vicinity probably has the best chance of verification of an Ike landfall. That said, the trend over the past day has been rightward, in the direction of the Houston-Galveston metro. I should also note that with a large, sprawling gyre such as Ike, upper level features can play a role in steering the hurricane. Satellite views clearly show the western edge of the subtropical high to be just west of Sabine Pass. You may also note that GOES imagery also depicts a shortwave and cold front approaching the Pacific Northwest. This feature will, as it progresses eastward, tend to erode the ridge further and act in sync with the equatorial moisture axis to its south) in turning Ike northward as the cyclone nears the shore near Port Aransas. Therefore, it makes sense to go to the right of the mean track scenario put forth by the entire array of computer versions. Being that the rightward limit is High Island, a point about one third of the way between the average NWP landfall point and the eastern bound supported by some of the tropical equations. So for this discussion Bay City TX is used as the entry to land. Because of the huge envelope associated with Ike, all sorts of watches and warnings will straddle the entire coastline from below Corpus Christi TX to Cameron LA during Friday and Saturday. Impacts From Expected Weather Rainfall: 4 - 8 inches or more within 225 miles of the landfall point and ultimate landward track, with points within 100 miles of the Ike trajectory seeing as much as 16 inches of rain.

Storm Surge: In excess of 15 feet in parts of Matagorda Bay and the shoreline of Galveston Island, with some swells well over 30 feet prior to landfall (around 8 AM Saturday). Some pulsations of surge in Galveston Bay and surrounding bayous and streams may reach 10 feet into portions of Brazoria, Galveston, and Harris counties through much of Saturday.

Winds: Towns of Matagorda, Bay City and Freeport may experience winds in excess of 135 mph on Saturday morning. Hurricane force winds may persist as far as 100 miles from the coast, mostly clustered around TX Route 6, US 290, Interstate 45 and perhaps US 59. Category 2 velocities could affect most of the Houston/Galveston metro area. Tropical Storm force displays may persist with the weakening circulation on later Saturday and Sunday as far north as the Red River Valley and the Arklatex vicinity.

Tornadoes: With its broad circulation, expected pristine banding features and a dry air intrusion, Ike by itself would be favored to generate many tornadoes along and to the east of its trajectory. However, with a frontal structure advancing and eventually merging with Ike (over SE OK on Sunday evening), the addition of vorticity and an in-situ dual jet stream display may increase the potential for multiple and damaging twisters across C, E TX, W LA, SW AR and SE OK.

Aftermath

I expect Ike to continue to the north and east with the front, providing severe weather, wind gusts, and heavy rainfall into portions of the Ohio Valley and the Northeast early next week. The addition of energy to the progressive trough will aid in cool advection, so much so that a polar air mass will reach as far south as the Bay of Campeche and Strait of Yucatan within a week from this writing.