Weatherdem's Weblog

Bridging climate science, citizens, and policy


Leave a comment

Atlantic Tropical Weather Update 9/4/08

[Update 10:30P MDT]:

There was nothing terribly critical with the NHC’s 11P update.

Tropcial Storm Hanna looks more and more certain to make landfall along the North Carolina coast as a Tropical Storm overnight Friday into Saturday.

The last part of Hurricane Ike‘s forecast (Tuesday night) hints at a possible southern Florida landfall, possibly as a major hurricane.  I don’t think the intensity models have properly accounted for these conditions.  Ike should pass over these cooler waters after he stops battling the northeasterly wind shear he’s currently facing.  As time has gone by, Ike’s official track at the end of the period hasn’t curved back toward the NW or N.  This means there is the possibility that Ike could roll over Florida and re-emerge over the Gulf of Mexico after Tuesday.  The suite of model track solutions still shows large variability by the third day.  One model continues to show a glancing landfall off Cuba’s north coast.  One shows Ike moving through the Florida Strait after running over the Bahamas.  Three keep Ike out in the Atlantic.  And one shows Ike moving nearly due west over the next five days.  Some fairly substantial discrepancies will have to be ironed out, and this should happen in the next day or two.

Tropical Storm Josephine has slowly started moving slightly north of due west, with no chance of affecting any kind of land within the next week.  Here are all the storms’ vitals:

Tropical Strom Hanna’s center is located at 26.5N, 76.3W; has maximum sustained winds of 65mph; is moving NW @ 14mph; and has a minimum pressure of 987mb.

Hurricane Ike’s center is located at 23.6N, 59.5W; still has maximum sustained winds of 135mph; is moving W @ 14mph; and has a minimum pressure of 945mb.

Tropical Storm Josephine’s center is located at 15.1N, 33.8W; has maximum sustained winds of 45mph; is moving WNW @ 10mph; and has a minimum pressure of 1002mb.

***

Earlier update and original post below the fold.

Continue reading

Advertisements


Leave a comment

Atlantic Tropical Weather Update 9/3/08

[Update 9:30P MDT]:

One major update among the range of updated information is available tonight. Forecasts are notoriously difficult for hurricanes. Ike exploded in the past eight hours. More details on him below. As usual, the updates are alphabetical.

Tropical Depression Gustav remains stuck over eastern Oklahoma/western Arkansas. There hasn’t been any change to his future.

Tropical Storm Hanna has maintained herself quite nicely in the face of very unfavorable environmental conditions. Her vitals include: center located at 23.2N, 72.1W; maximum sustained winds of 65mph; moving NNW @ 12mph; minimum pressure of 989mb. So Hanna has begun moving just west of north. Her path should move a little more west in the next day and continue thereafter.

There is some distance between Hanna and the Bahama Islands. They’re not experiencing drenching rains so much as they’re seeing winds just under tropical storm strength that get gusty at times and the surf is getting kicked up a bit. The official intensity forecast calls for Hanna to reintensify to hurricane strength by Friday morning. As you’ll read below, her intensity could jump up unexpectedly as she moves over warmer, but shallower, waters on her way toward the U.S. By Friday night, Hanna should be located off the coast of South Carolina. The next day’s worth of motion and investigation will really affect her exact path and potential landfall sites.

Somewhere near this same time, she should once again shift her trajectory back toward the north, then the northeast. This could keep her from making landfall over South Carolina and instead do so over eastern North Carolina. The official track forecast still keeps Hanna close to either the ocean or the shore, depending upon the eventual track. Regardless, she looks likely to affect a lot of square miles as she makes her way northeast from North Carolina, possibly getting up toward New Jersey by Saturday night as a Tropical Storm.

Hanna should continue to make her way around the periphery of the high pressure system responsible for her steering. She could affect the remainder of the New England region and southeastern Canada before she moves away from land around 50N by next Monday.

Okay – the big news of the day. Tropical Storm Ike became Hurricane Ike earlier this afternoon. Since then, his intensity has simply exploded. Hurricane Ike is now the third major hurricane of the 2008 Atlantic season. In fact, Ike blew through Categories 2 and 3. He is now a Category 4 storm! Here are his vitals as of tonight:

Center located at 22.1N, 54.1W; maximum sustained winds of 135mph!; moving WNW @ 17mph; minimum pressure of 948mb!! I’ll look for the official measurement, but it seems to me like Ike’s pressure dropped 36mb in about 6 hours. That is incredible intensification and is indicative of the massive heat content available in the Atlantic Ocean. Beneficial environmental conditions haven’t hurt him any, obviously. Ike still has a very small, tight eye on satellite imagery. Additional intensification is possible in the next 12 hours, but any further changes will be dependent on eye-wall replacement cycles.

In between 12 and 72 hours (.5 – 3 days), Hurricane Ike will experience northeasterly shear as the upper level low that was affecting Hanna makes its way eastward across the Atlantic. The official intensity forecast calls for slight weakening during that time period. Ike’s official track forecast calls for him to continue his general northwestward motion over the next 24-36 hours. Starting Friday morning, Ike should curve back toward the southwest as a ridge restrengthens after the low passes through the region. Ike should pass well north of Puerto Rico Friday night through Saturday morning. Saturday night could see Ike north of the Dominican Republic, again at a good distance.

The ridge that should push Ike southward in the 2-4 day time period should shift around late day 4 and then in day 5 as well. Similar to Hanna’s track around the ridge, Ike should move around the southwestern periphery of the same feature. That means Ike could move through the southern portion of the Bahamas (not much change from earlier) on his way through the central Islands by the time Monday night rolls around. During the 4-5 day time period, the official forecast calls for Ike to reintensify back to a Category 4 storm.

So starting at the beginning of next week, things are going to get exciting for the U.S. Will Ike make landfall over Cuba? Will he make landfall over the U.S.? Will he move through the Florida strait into the Gulf of Mexico? If he makes landfall over the U.S., where will that occur? Will he follow Hanna’s path around the edge of the ridge and possibly miss land altogether? Also of importance: Hanna has stirred up the Atlantic around the Bahamas for quite some time now. Ike could encounter much cooler surface waters than Hanna had available to her. Will that work to weaken Ike somewhat or quite a bit? There are lots of questions. We’ll just have to keep watching.

Tropical Storm Josephine’s future hasn’t changed since this afternoon. Let’s start with her current vitals: center located at 13.9N, 30.7W; maximum sustained winds of 50mph; moving W @ 12mph; minimum pressure of 1000mb. Josephine is still forecasted to begin moving more north of west in the next couple of days, albeit a little more slowly than her current speed. She is still forecasted to weaken to Tropical Depression status by Saturday, if not sooner.

***

Continue reading


Leave a comment

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.

Continue reading


Leave a comment

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.

Continue reading


Leave a comment

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.

Continue reading


Leave a comment

Atlantic Tropical Weather Update 8/30/08

Hurricane Gustav has passed over the deep, very warm waters between Jamaica and Cuba. In doing so, he rapidly strengthened overnight from a Category 1 hurricane to a Category 3 storm this morning, making him the second major hurricane of the 2008 Atlantic season. Bertha was the other major hurricane, but remained well out to sea her entire lifetime. Gustav’s vitals as of 8:30A MDT:

Center located at 20.8N, 81.6W; maximum sustained winds of 120mph; moving NW @ 11mph; minimum pressure is down all the way to 955mb, which is 33mb less than the reading yesterday. That is quite the rapid intensification. In fact, since the pressure has continued to drop steadily this morning, expect Gustav to strengthen even further today before eye-wall replacement cycles, a slightly cooler pool of water and the island of Cuba work to weaken him somewhat.

Gustav should still make landfall over Cuba later tonight as a Category 3 storm. A solid eye-wall did develop overnight. Gustav has an impressive outflowing cloud shield. Hurricane force winds were found on the northeast quadrant on an earlier hurricane hunter flight. As they get going again today, a clearer picture of where they are found will be available. Tropical Storm force winds extend all the way to Cuba, a decent distance from the storm’s center. Western Cuba is under a Hurricane Warning today.

Model solutions have come to closer agreement as of today. There is a much narrower band encompassing the solutions through the Gulf of Mexico, which Gustav will enter 12-24 hours from now. While Gustav crosses the central Gulf, he is still forecasted to overrun the Gulf Loop Current’s warmest stretch. The model intensity forecast has him strengthening to a Category 4 hurricane during this time, but I wouldn’t be surprised to see him go all the way to a Category 5. After that, there is very good agreement about the likely landfall location: the middle of the Louisiana coast. He should make landfall between Morgan City and Lake Charles. The timing is coming into better focus. The suite of models are also in pretty good agreement that the landfall could occur Monday night.

Post-landfall may not offer a better story than during landfall. Due to the strength and orientation of the ridge that will remain over the eastern U.S., Gustav could stall over Louisiana. We’ve already dealt with one slow moving storm: Fay dropped incredible amounts of rainfall over Florida just a week or so ago. Gustav shouldn’t dump quite that much rain, but the longer he lingers, the more flooding far inland will be a concern. New Orleans residents are smartly already evacuating. I’m sure other Gulf coast residents will follow similar measures throughout the next two days.

Continue reading