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Atlantic Tropical Weather Update 9/2/08

Lots of changes in the Atlantic basin since yesterday. Gustav has continued to weaken, from Hurricane strength down through Tropical Storm and is a Tropical Depression this morning over the TX/LA border. Hanna strengthened to a Hurricane, then weakened back to a Tropical Storm. Then, Tropical Depression Nine formed between the Leeward Islands and the Cape Verde Islands. Then T.D. 9 strengthened and was named Tropical Storm Ike. Then T.D. 10 organized from Invest-99 between the Cape Verde Islands and Africa. Development didn’t stop there: T.D. 10 strengthened and Tropical Storm Josephine formed. That’s all in less than 18 hours. The Atlantic basin is pretty much full of storms.

Let’s start with Tropical Depression Gustav’s vitals: center located at 31.7N, 93.4W; maximum sustained winds of 35mph; moving NW @ 10mph; minimum pressure of 985mb. Gustav’s main threat now is lots of rain that could cause flooding. A secondary threat remains tornadoes. Gustav is forecasted to curve toward the northeast over the next five days, but the distance covered shouldn’t be too great. He should move into northeast Texas, southeast Oklahoma, then western Arkansas by early Friday morning.

Yesterday, Hanna was a Category 1 hurricane. She stalled off the eastern side of the Bahamas as her steering currents weakened. She followed by weakening back to a Tropical Storm, where she remains this morning. Steering has picked back up this morning and Hanna is back on the move. Her vitals: center located at 21.0N, 73.5W; maximum sustained winds of 70mph; moving WSW @ 5mph; minimum pressure of 987mb.

Hanna is forecasted to begin moving back toward the northwest later today, then continue that general movement through the next few days. She is also forecasted to regain hurricane strength by tomorrow afternoon as she moves through the Bahamas. From Thursday to Friday, Hanna should be moving by the east coast of Florida, but no landfall is expected on that state. Sometime during the day on Friday, Hanna is expected to come ashore along the Georgia border, an event that is very rare due to the orientation of the coast and the climatological movement of storms along the eastern seaboard. By the time Hanna reaches the Georgia/South Carolina border, the model track solutions diverge. Some show her moving into West Virginia before curving toward the northeast. Some show her moving through the Carolinas before turning northeast and along the east coast. That’s some time away, so the details will have to wait.

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Atlantic Tropical Weather Update 9/1/08

[Update 11:45A MDT]:

Tropical Storm Hanna has strengthened to a Category 1 hurricane.  An Air Force reconnaisance plane investigating the storm found winds strong enough at flight level to support the decision to characterize the storm as a hurricane.  Her updated vitals:

Center located at 22.4N, 72.6W; maximum sustained winds of 75mph (just over category 1 threshold); moving WSW @ 4mph; minimum pressure of 985mb (9mb less than the previous update).  The lowering pressure should allow Hanna to continue to slowly strengthen into a moderate Category 1 hurricane.  The intensity forecast has been updated to reflect this status in the short term.  At this time, the models are not indicating a strengthening to Category 2 strength.

***

Hurricane Gustav made landfall within the past hour or two (currently 9:30A MDT) on Louisiana’s southern coast, near Cocodrie, Louisiana, which is south of Houma, Louisiana.  He made landfall as a strong Category 2 storm.  Reports are coming in that levees in New Orleans, to Cocodrie’s north, are being overtopped by the storm surge and waves.  I’m sure additional reports will come in throughout the day.  His vitals:

Center located near 29.2N, 90.8W; maximum sustained winds of 110mph; moving NW @ 14mph; minimum pressure of 955mb.  Those sustained winds are the threshold between a Category 2 and Category 3 storm.

Gustav’s future looks radically different than it did last night in the long-term.  He is expected to slow down over the next day or so as he moves across Louisiana and eastern Texas, weakening the entire way.  Between Tuesday and Wednesday, Gustav should turn toward the north (instead of the south, as was indicated last night) and his forward speed should continue to decrease.  Friday could see Gustav still moving slowly to the north into Oklahoma.  By the end of the week, another synoptic trough should be moving across the United States.  That trough right now looks less robust than the one currently making its way from west to east, but Gustav’s remnants should get caught up in the larger scale flow and advected out of the Texas/Oklahoma region.

So beyond additional levee failures in the New Orleans area, the main threat from Gustav will gradually shift toward flooding as he stalls and rain falls over the same area for many hours.

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Atlantic Tropical Weather Update 8/31/08

Hurricane Gustav came off the western portion of Cuba last night as a Category 4 hurricane and maintained that strength while continuing northwest. It appears that interaction with the landmass caused Gustav to weaken slightly since then. As of this morning, Gustav has weakened to a still very dangerous Category 3 storm. Starting with his vitals:

Center located at 25.3N, 86.0W; maximum sustained winds of 120mph; moving NW @ 17mph; minimum pressure of 960mb, about 20mb higher than the last time I looked near 12A MDT.

Gustav’s impressive satellite signature yesterday has degraded so far today. There is no longer a clear eye portion of the storm. Also, the convection and outflow isn’t as symmetric as it was late last night. The strongest convection looks to be confined to the southwestern portion of the storm.

What’s next for Gustav? He is still heading straight for the northern Gulf coast. As the hours tick away, his most likely landfall site is being forecasted with more confidence. Somewhat surprisingly, that location remains southern Louisiana, perhaps a bit to the east of where I thought he would strike the past two days. It looks more likely that the site will be close to New Iberia, LA. Models are forecasting a slight re-increase of strength back to Category 4 status while Gustav is still over the Gulf. Prior to landfall, his strength should begin slowly decreasing and continue to do so after landfall. Landfall is expected to occur during the day on Monday, currently sometime after 8A CDT. Due to the influence of the ridge of high pressure over the eastern U.S., his forward speed should decrease and the possibility of him stalling over Louisiana or Texas remains high.

Storm surge from Gustav is expected all along the northern Gulf coast. A maximum of 12-15 feet of storm surge is possible near the mouth of the Mississippi River and east of New Orleans. The height of surge east and west of this region decreases from there, with up to 12 feet forecasted a good distance away from the River, out toward Abbeville to the west and Biloxi, MS to the east. Combined with rain from convective bands, flooding then becomes a major risk from this storm across a very wide area. The initial storm surge and winds will weaken infrastructure and a stalled storm will only add to the challenges facing those who live and those who will help clean up in the region. Based on Gustav’s current projected path and expected effects, I don’t think the situation looks good for the New Orleans area. Damage from wind and flooding should occur once again. It is obviously too early to tell just how extensive that damage will be, which means that officials along the Gulf coast should be congratulated on acting promptly to move residents away from the area.

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