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Atlantic Tropical Weather Update 9/2/08

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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.

Onto T.D. 9, now known as Tropical Storm Ike. His vitals: center located at 18.9N, 45.0W; maximum sustained winds of 60mph; moving W @ 18mph!; minimum pressure of 1002mb. Ike has stong convection on the east side of the storm. He’s in a good environment for further development.

Ike’s track forecast envelope is very tight over the next three days and is pretty narrow in five days. Right now, it looks like Ike will primarily affect Caribbean islands. The official forecast calls for Ike to become a hurricane sometime tomorrow. By Friday, Ike should be north of the Leeward Islands, still moving west. By Saturday, Ike should be northwest of Puerto Rico and northeast of Hispanola. Sunday could see Ike affecting the southern Bahamas as Ike looks to be taking aim at Cuba. The models forecast Ike to slowly strengthen throughout this time period. Whether he becomes a major hurricane or not is not clear at this time.

The tenth tropical storm of the season also formed in the past 24 hours. Tropical Depression 10 formed off the west coast of Africa, then strengthened in the past few hours (based on satellite measurements) to tropical storm status. Tropcial Storm Josephine is currently located just southwest of the Cape Verde Islands. That center is located at 13.2N, 25.3W; she has maximum sustained winds of 40mph; is moving W @ 15mph; and a minimum pressure of approximately 1005mb.

Josephine is forecasted to begin moving in a more NW motion later today and continue that path over the next 3+ days. She could reach 15N by tomorrow night, and 20N by Saturday morning. By Sunday, the official track forecast puts her near 21N, 47W, which is still very far out to sea. She isn’t forecasted to strengthen to a hurricane during that time period.

***

[Update 4:00P MDT]:

The NHC issued some updated information this afternoon. What does it show?

Tropical Depression Gustav is centered near 33.0N, 93.9W; moving NNW @ 8mph; sustained winds of 20mph; minimum pressure of 993mb. Rain and convective bands continue to spiral around the surface low. Four to ten additional inches of rain are possible for a wide area. Gustav is forecasted to dissipate in the next three days.

Tropical Storm Hanna has taken a beating from vertical wind shear and Gustav’s outflow from the past two days. She has continued to slowly weaken throughout the day, and her disorganization has been evident on satellite imagery. Here are her vitals as of this afternoon:

Center located near 20.4N, 72.7W; maximum sustained winds between 60 and 65mph; moving SSE @ 4mph; minimum pressure of 987mb. The shear should dissipate in 24 or so more hours. Additionally, the nearby ridge should restrengthen, which would steer Hanna toward the northwest.

Due to her shear environment and meandering near the Bahamas, and given the lack of definitive steering over the next day, the track forecast envelope is a little more uncertain than it appeared this morning. Hanna is still expected to move steadily northwestward over the next several days. Now though, a couple models show her gently moving ashore over Florida, while another has her making landfall over North Carolina again. The remainder show a Georgia/South Carolina landfall in about three days’ time. The official track forecast calls for Hanna to make landfall over South Carolina Friday afternoon/evening. A steady strengthening could occur during this time period, but I’m no longer sure Hanna will achieve Category 1 hurricane status again before landfall. The chances are equal of that occurring as well as maintaining tropical storm strength. The next day or so should provide more clues.

Tropical Storm Ike still looks healthy. Here are his vitals: center located near 19.2N, 46.3W; maximum sustained winds of 65mph (somewhat stronger than this morning); moving W @ 17mph!; minimum pressure estimated to be 996mb. A band of deep convection has wrapped around the center since this morning, making Ike look more organized on satellite imagery. It also looks like he’s venting outflow pretty efficiently now too.

Ike’s center has moved slightly more north today, but most of his motion has been toward the west. Over the next three days, that general easterly track could be modified by some gentle motion toward the north, ending up near 22-23N by Friday. As I wrote this morning, that would put Ike north of the Leeward Islands at that time. Thereafter, his track is officially forecasted to move just south of west as he maintains his strong forward speed. Saturday could find him north of Hispanola and by Sunday, Ike could still be bearing down on Cuba. He is officially forecasted to stregthen to a Category 1 hurricane over the next 12 hours. Keep in mind that some intensifications occur very rapidly. Ike is in a good environment for intensification though, so he could get to Category 2 strength by the time Friday rolls around.

Tropical Storm Josephine also looks pretty concentric on satellite imagery, but her cloud tops aren’t as cold as Ike’s. She is located near 13.7N, 25.9W; she has maximum sustained winds of about 50mph; she is moving WNW @ 14mph; her minimum pressure is estimated to be 1000mb. So her winds are a little stronger tonight and her pressure is likely a little lower, indicating that some further intensification could occur in the near future.

The official intensity forecast calls for her to strengthen in about 24 hours time as she continues to move toward the WNW. In three days’ time, she is forecasted to be centered near 19N, 40W. And in five days’ time, she should be near 22.5N, 49W. She could weaken during that time as an upper-level trough moves by her to the north, increasing her local vertical wind shear. Her projected path also takes her over slightly cooler surface waters, which should work to weaken her also.

***

[Update 10P MDT]:

Today’s last NHC update has been issued. Four areas of interest are included.

Starting with Tropical Depression Gustav, there isn’t much new to report. The remaining disturbance hasn’t moved much all day, meaning the lingering rain bands have really soaked a wide area. The disturbance is forecasted to be absorbed in the larger-scale flow within 24 hours.

Tropical Storm Hanna has moved in a counterclockwise motion today. The NHC is keeping her official strength near where it has been all day, but this storm is really looking unimpressive tonight. Another plane is scheduled to investigate the system in a few hours. Hanna has battled some shear all day today, but that shear is expected to shift over the next day or so, which could act to help restrengthen the storm. Here are her vitals:

Hanna’s center is located near 20.5N, 72.4W; maximum sustained winds of 65mph; is more or less stationary; minimum pressure of 988mb.

Hanna’s forecasted track continues to shift along with the differences in motion seen today. She is forecasted to move northward over the next 12-24 hours, with a gradual turn toward the northwest near the 24 hour period. This motion should continue in the 2-4 day time period, taking Hanna along the northeast shores of the Bahama Islands. She could finally move away from the Bahamas after Friday night on her way toward the U.S. east coast. The model track envelope remains a little wide in the 4-5 day range, just as it did earlier today. She could make landfall anywhere from Georgia to North Carolina. The official forecast continues to show Hanna doing so over South Carolina between Beaufort and Charleston.

Moving along to Tropical Storm Ike, here are his vitals tonight:

Center located near 19.9N, 47.9W; maximum sustained winds of 65mph; moving WNW @ 17mph. So Ike is still moving quite rapidly across the basin.

Tropical Storm Ike is forecasted to move just north of west over the next two days, then more due westerly in day three before turning slightly south of west in days four and five. Ike is in a good environment for intensification and could reach Category 1 hurricane status by tomorrow morning. Gradual intensification is forecasted over the next three days, and Ike could be a Category 2 storm by Friday night. The official forecast puts Ike very close to Cuba by Sunday night, having pushed through the southern Bahamas Saturday night through Sunday.

Tropical Storm Josephine also continues to make her away across the Atlantic basin. Here are her vitals tonight:

Center located near 13.6N, 26.8W; maximum sustained winds of 50mph; moving W @ 12mph; minimum pressure of 1000mb.

Josephine is still forecasted to start moving north of west in the next 12-24 hours. She should remain well out to sea from any land through Sunday night. She isn’t expected to strengthen during that time to a more significant system, as she is likely to battle shear as an upper-level trough moves west to east across the Atlantic. That’s a change from earlier forecasts.

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