Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf
Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.
Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.
Leslie's impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.
Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.
Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.
Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.
Figure 3. Morning satellite image of Tropical Storm Michael.
Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.
Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.
Jeff Masters
Reader Comments
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Let me guess, you want it to go right over your house, too?
I would be perfectly fine to not have a cat 5 for another 5 years. I'm also sure that 99.999999999% of the western Atlantic coast would be happy with it, too.
Didn't recognize you without the Flying Elvis!
Yep, the service ceiling is 45k, but it will do 50k if it has to. I've been wondering when the were going to fly the UAV. I think this really the future for HH aircraft.
That would be .000000001% :)
Good link, thanks. I knew it was some high altitude microwave & such but that might help find some of the data.
This is almost like a controlled satellite, but low enough your dropsondes don't burn up.
That's one consideration, I'm sure, but the range, sensor capabilities, and higher ceiling are really selling points. The Global Hawk can put a Hellfire missile right down the chimney of a house anywhere from 500 to 50,000 feet, so looking into a hurricane should be relatively easy with the sensor package on those babies. :)
Link
I am not predicting 90L to do so, but it does appear to be still sinking south. If by some chance 90L does happen to get south of 24N, and is no more than a TD, it may not get whisked off towards the east with that trough.
One thing you regular bloggers should be proud of is the amount of education you give those of us who follow the hurricanes - I learn more here every year than I do anywhere else.
Re: making money following hurricanes, it is a hard thing to explain to people that one gets a little excited when the hurricanes start looking like they'll make landfall in the US - do not wish harm to anyone, but do look forward to weeks/months of really good work for my husband when he goes to help with the power restoration. We can't do a lot to help here in MN, so it feels like I'm sending help to the people affected; hubs calls and says, "Well, we just LIT UP A TOWN!" He also likes to help and really enjoys getting electricity back up for people who lose it during storms.
Umm No thanks ...
best chance for a five would be latter half of the the peak
2nd week of october on
side winder moving ne ward
from the sw carb nw carb
cen boc in gom
Thank goodness there are people who enjoy doing it, I can't imagine where we'd be after a storm if all the power company workers were just in it for the money and took no personal satisfaction in the work. Tell him that we do appreciate it, and most people who haven't been through a big storm can't imagine how much we do. It's just so much easier to deal with everything else when you can have lights and AC vs. a hot and humid house for days to weeks after, oppressively dark both from the lack of power and from shutters if you put them up.
It's amazing how just having light that isn't coming from a candle or flashlight can cheer you after a storm. Even if it's also showing you the extent of the damage you've taken more clearly... :p
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