Weathermandan's Blog
Tropical Update - Double Trouble: Gustav and Hanna strengthe, churn towards the U.S.
Posted by: Weathermandan, 3:36 AM GMT on August 31, 2008 +0
Hurricane Gustav


Hurricane Gustav has weakened slightly after passing over western Cuba this afeternoon/evening, with maximum sustained winds now at 140 mph. However, restrengthening is already beginning as the eye of the storm re-emerges back over water into the southern Gulf of Mexico. Areas of deeper convection are appearing on satellite (as of ~11 PM Eastern Time) on both the west and east sides of Gustav's eyewall. I would expect Gustav's intensity to peak at about 165 mph sometime tomorrow, which would make it an extremely dangerous category 5 storm. It will not hold on to category 5 status, however. Lower oceanic heat content and slight wind shear from an approaching trough will gradually weaken the storm through landfall.

After making a brief right turn overnight, Gustav will resume a northwestward path across the Gulf of Mexico, approaching the Lousiana coast Monday afternoon and evening. The storm is expected to slow as it approaches land and turn to the left, resulting in a rather expansive area and prolonged period of rough seas, extensive storm surge (possibly exceeding 20 feet in some areas) and high winds. The slowing of the storm will also result in potentially catastrophic flooding rainfall across inland areas of Louisiana and Texas. The storm will likely make landfall in southwestern Lousiana, perhaps the extreme upper Texas coast if the ridge steering Gustav strengthens further, which is definitely possible.

Gustav at landfall is expected to be a major hurricane, but weaker than it is now. My best guess would be for sustained winds of around 120-125 mph at landfall, and a landfall location somewhere between High Island, Texas, and Marsh Island, Louisiana. However, significant to severe surge is still likely across southeastern Louisiana, including the New Orleans/Lake Ponchartrain area, with substanial surge/squally weather/and isolated tornadoes as far east as the western Florida Panhandle, including Mobile Bay and Pensacola. This is likely to be a large and powerful storm at landfall capable of producing significant damage to an extensive area.

Also of note is the fact that Hurricane Gustav will be passing over an area of the northwestern Gulf that contains over 3500 oil wells.

In the short term, Gustav's outer rainbands will produce gusty winds of 50 to 60 mph, isolated tornadoes/waterspouts, and rainfall of 2 to 4 inches, with locally as much as 10 inches possible in areas of persistent, heavier convection.

New Orleans is already under a mandatory evacuation, and similar orders will likely be issued later tonight or tomorrow morning for the remaining areas of the southern Louisiana coastline, perhaps as far west as the Houston/Galveston area.

Areas from Houston, Texas, to Pensacola, Florida, should closely monitor the progess of dangerous category four Hurricane Gustav.

Tropical Storm Hanna


Further east, into the western Atlantic, Tropical Storm Hanna continues to persist despite moderate southwesterly wind shear. As of 11 PM Eastern Time, Hanna still had maximum sustained winds near 50 mph. This strength will likely hold overnight and then increase somewhat during the day Sunday as shear diminishes. Hanna could approach hurricane strength as it approaches the Turks and Caicos and southeastern Bahamas Sunday night or early Monday, before more wind shear impedes development of this system, this time from a northerly direction.

Hanna is expected to stall out and loop around over the Bahamas early this week, before shear diminishes and Hanna resumes a northwestward heading, strengthening as it passes over the Gulf Stream into a hurricane by the middle to latter part of next week. By late next week, Hanna could very well have its sights set on the Carolinas, as a significant, growing storm (GFS forecast model indicates a major hurricane approaching the Carolina coast from the south by next Friday).

All interests along the eastern Seaboard from Florida to southern New England should monitor the prgress of Tropical Storm Hanna.

Mid-Atlantic Tropical Wave


Another rather persistent tropical wave in the central Atlantic, about midway between the Lesser Antilles and the west coast of Africa, continues to be disrupted greatly by westerly shear. Significant development of this system is not expected over the next couple of days as if moves toward the west.

East-Atlantic Tropical Low (Invest 97L)


Although convection has temporarily weakend in assocation with low pressure moving away from the southwestern Cape Verde islands, a moist, low-shear environment couple with the relatively organized cyclonic circulation near the surface of this storm should lead to slow development into this season's ninth named storm through early next week. In about 72 hours, I expect this system to have become Tropical Storm Ike, and be churning about midway between the Lesser Antilles and the west coast of Africa.

Other organized tropical waves and associated circulations continue to move towards the west coast of Africa, and these will be monitored for possible development as the emerge into the open Atlantic through the upcoming week.
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