About Jeff Masters
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
Disorganized Leslie headed towards Bermuda
By: Dr. Jeff Masters , 4:18 PM GMT on September 03, 2012
Tropical Storm Leslie continues to struggle with moderately high wind shear of 15 - 20 knots, due to strong upper-level winds out of the northwest. The shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm. These thunderstorms are as far removed from the center as we've so far with Leslie, as seen on satellite loops. According to the latest SHIPS model forecast, the shear is expected to stay moderately high through Tuesday night, then drop to the low category, 5 - 10 knots, by Wednesday night. At that time, Leslie will be over warm ocean waters of 29°C, and the reduction in shear and warm waters should allow Leslie to intensify into at least a Category 1 hurricane by Friday, as predicted by most of the intensity forecast models. Intensification to a stronger storm may be hampered by its slow motion, which will cause Leslie to churn up cool water from the depths that will slow intensification. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Saturday, as predicted by the HWRF and LGEM models. Steering currents for Leslie are expected to be weak on Tuesday - Friday, as Leslie gets stuck between two upper level lows. The latest guidance from our top computer continues to show Leslie making a very close pass by Bermuda on Saturday, and that island can expect a 3-day period of rough weather Friday through Sunday. 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. This trough should be strong enough to pull Leslie quickly to the north on Saturday and Sunday, and Leslie may be close enough to the coast that the storm will make landfall in Canada on Monday, September 10. None of the reliable models have shown that a direct hit on New England will occur, but we can't rule that possibility out yet. The most likely long-term fate of Leslie will be for it to miss land entirely and brush by the coasts of Nova Scotia and Newfoundland, but any forecast of what a tropical cyclone might do a full seven days in advance is pretty speculative. Regardless, Leslie will bring an extended period of high waves to Bermuda, the U.S. East Coast, and Nova Scotia and Newfoundland this week. These waves will be capable of causing significant beach erosion and dangerous rip currents.
Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center is fully exposed to view, thanks to strong northwest winds creating 15 - 20 knots of wind shear.
Invest 99L in the Central Atlantic
A small extratropical low pressure system that got cut off from the jet stream and is now spinning away in the Central Atlantic, near 26°N 42°W, (Invest 99L), is headed west at 10 mph, and has developed a small amount of heavy thunderstorm activity. This storm is not a threat to any land areas, and in their 8 am EDT Tropical Weather Outlook on Monday, NHC gave 99L a 30% chance of developing into a tropical cyclone by Wednesday morning.
Jeff Masters
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Reader Comments
Category 6™
1322. TropicalAnalystwx13
1321. stormpetrol
1320. Thrawst
1319. CloudGatherer
Never been a better illustration as to why our current classification method stinks. Saffir-Simpson shows no difference, but these two storms couldn't be more dissimilar.
1318. AussieStorm
How about a two number system classification. Isaac was a Cat 1 wind wise but a cat 3 surge wise, so that would make it a Cat 1.S3
Ike was a Cat 2 on landfall but had a surge of a Cat 4, so that would make it a Cat 2.S4
Irene on the other had was a Cat 1 on landfall and only brought minimal surge so that would make it a Cat 1.S1
Just a few more thoughts
1317. PuntaGordaPete
The HSI is close to useless for ordinary people. It is a measure of financial impact for the insurance industry and a measure of assistance needed for government and non-government agencies. Ordinary folks, those who need to prepare and evacuate, don't really care if someone else 200 miles away is also impacted. They care about maximum potential severity at their location.
1316. TropicalAnalystwx13
Kirk was close to high wind shear and dry air as well. Here is the first intensity forecast for Kirk by the NHC:
FORECAST POSITIONS AND MAX WINDS
INIT 28/2100Z 23.8N 43.9W 30 KT 35 MPH
12H 29/0600Z 24.1N 45.3W 35 KT 40 MPH
24H 29/1800Z 24.3N 47.4W 35 KT 40 MPH
36H 30/0600Z 24.6N 49.6W 35 KT 40 MPH
48H 30/1800Z 25.3N 51.7W 35 KT 40 MPH
72H 31/1800Z 27.5N 55.5W 35 KT 40 MPH
96H 01/1800Z 32.5N 55.0W 35 KT 40 MPH
120H 02/1800Z 40.0N 48.0W 35 KT 40 MPH
1315. AussieStorm
I see the NHC have upped their 120hr forecast intensity from 100mph to 105mph. Up-welling anyone???
DUE TO THE LARGE SIZE OF
LESLIE AND ITS EXPECTED SLOW MOTION...LARGE SWELLS PROPAGATING AWAY
FROM THE TROPICAL CYCLONE WILL AFFECT BERMUDA AND NEARLY ALL OF
THE U.S. EAST COAST FOR MUCH OF THIS WEEK.
1314. 7544
1313. RitaEvac
1312. jeffs713
Yeah, but 13L is really close to an area of higher shear (to the SE, per CIMSS), and dry air (to the west). With its size, it will be highly sensitive to both shear and dry air - and the mid-level shear doesn't look very favorable either.
I think the NHC forecast is decent, so I wouldn't expect anything beyond a low-level TS, at best.
1311. SFLWeatherman
Another round of heavy rainfall with some strong to even severe thunderstorms will be possible today...especially over the interior and east coast areas this afternoon/evening.
1310. Progster
Has snow ever been reported at Perth?
1309. AussieStorm
The next one is going to bring very cold air behind it but it wont last long with a big as high setting in pretty quickly.
1308. VR46L
1307. WxLogic
If it were to be the case (in the short term)... I would expect one at 2AM ET at the earliest. Since around this time is when I would expect most of the Mid/Low level energy from the remnants of Isaac to be in the N/NE GOM.
1306. Progster
The next cold front approaching SW Australia looks pretty nasty too. You've got some big snakes on the southern Jet Rossby wave.
1305. Tropicsweatherpr
Dont forget the possible CV development that the models also develop.
1304. RTSplayer
So as you can see, I'm interested in alternative ranking systems for the severity of storms, which are easy enough to calculate so that meteorologists can communicate the destructive potential to the audience, so that they can make better decisions.
Current practices are to pick 2 or 3 analog SS scale rated storms and compare them to the expected landfall. With the occasional mentioning of "well this one is bigger in area, so it might be a little worse".
I think that doesn't go far enough.
I think they should pick 2 or 3 analogs from each of 3 rating systems for expected landfall rating:
Predicted SS category to maintain continuity.
Predicted IKE value at landfall.
Predicted HSI value at landfall.
Pick 2 or 3 analogs from each ranking system, with a maximum of 1 overlapping storm across ranking systems.
Example, since Katrina is a classic example of where no one ranking system is sufficient, you could use Katrina's landfall as an analog in all 3 ranking systems during a forecast, but you can't use any more overlaps. This would allow 2 additional analogs from each ranking system, which cannot overlap.
The benefits of this would be the ability to better select analog storms, the public does not necessarily need to know how they were selected, but it would help to go ahead and tell them.
For example, if you tell somebody Katrina landfall was a 36, Andrew landfall was no higher than 33, and "Storm X" is forecast to make landfall as approximately a 32, then everybody knows to evacuate, regardless of it's exact SS ranking.
Whereas if you say, "Well, it'll make landfall as a 115mph cat 3," lots of people will just ride it out, as was even the case with Rita and Katrina (ironically).
1303. GeoffreyWPB
1302. GetReal
T-storm activity coverage and intensity on the increase, in NW Florida and the adjacent coastal waters, as the remnants of Isaac make a run towards the GOM. There is still a hint of a cyclonic twist, and this maybe of some interest 36 hours from now.
1301. yqt1001
From the discussion:
THE FUTURE STRENGTH OF THE DEPRESSION IS NOT AN EASY PREDICTION AS
IT IS VERY CLOSE TO SOME STRONG NORTHWESTERLY SHEAR. HOWEVER...THE
BULK OF THE MODEL GUIDANCE IS NOW INDICATING THAT THIS SHEAR WILL
STAY AWAY FROM THE CYCLONE...WITH LITTLE CHANGE IN THE ENVIRONMENT
PROBABLE FOR THE NEXT COUPLE OF DAYS WHILE THE CYCLONE REMAINS OVER
WARM WATERS.
1300. AussieStorm
Late winter/early spring strong fronts are common. Changing of the seasons can bring big changes.
1299. RitaEvac
Was down in Galveston when storms rolled in Saturday on the seawall. Was at the Spot eating and watched that white draped curtain (rain shaft) come in over the water, was cool seeing it.
1298. RTSplayer
Current practices are to pick 2 or 3 analog SS scale rated storms and compare them to the expected landfall. With the occasional mentioning of "well this one is bigger in area, so it might be a little worse".
I think that doesn't go far enough.
I think they should pick 2 or 3 analogs from each of 3 rating systems for expected landfall rating:
Predicted SS category to maintain continuity.
Predicted IKE value at landfall.
Predicted HSI value at landfall.
Pick 2 or 3 analogs from each ranking system, with a maximum of 1 overlapping storm across ranking systems.
Example, since Katrina is a classic example of where no one ranking system is sufficient, you could use Katrina's landfall as an analog in all 3 ranking systems during a forecast, but you can't use any more overlaps. This would allow 2 additional analogs from each ranking system, which cannot overlap.
The benefits of this would be the ability to better select analog storms, the public does not necessarily need to know how they were selected, but it would help to go ahead and tell them.
For example, if you tell somebody Katrina landfall was a 36, Andrew landfall was no higher than 33, and "Storm X" is forecast to make landfall as approximately a 32, then everybody knows to evacuate, regardless of it's exact SS ranking.
Whereas if you say, "Well, it'll make landfall as a 115mph cat 3," lots of people will just ride it out, as was even the case with Rita and Katrina (ironically).
1297. CybrTeddy
Who knows, Kirk was also a small system that was only predicted to be a moderate TS at best.
1296. GeorgiaStormz
Does my avatar apply to you as well?
Tropical Thunderstorm Michael
Hey, it did re-cover its COC and has a nice Thunderstorm... i mean CDO, over the center
1295. AussieStorm
What are Leslie's number.
T2.5/3.5 12L LESLIE
T2.5/2.5 13L NONAME
1294. unknowncomic
1293. jeffs713
Yep. I will admit, I was kinda hoping to keep the routine of this year with all of the male storms being more intense (with the exception of Alberto).
1292. unknowncomic
1291. CybrTeddy
Exposed COC is not usually a hindrance for an upgrade as long as the convection is somewhat close to the COC, and location is never a reason to not upgrade. Per ATCF, unless the NHC changes it's mind, we have Michael.
1290. jeffs713
I'm guessing I picked up about 2/3 of an inch. Both of the PWS nearest to me either were missed by the storm that hit my house (it was tiny, but rather intense), or weren't online Saturday. DW Hooks airport picked up 1.18", but it got one cell that just barely missed my house. In any case, it was enough that I don't have to water this week. :)
1289. GeoffreyWPB
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0945 AM EDT TUE 04 SEPTEMBER 2012
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 05/1100Z TO 06/1100Z SEPTEMBER 2012
TCPOD NUMBER.....12-108
I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK: FIX OF TROPICAL STORM LESLIE
AT 06/1800Z NEAR 27.0N 62.8W.
1288. jeffs713
I don't agree with that, as TD13 is partially exposed, and WAAAAAAY out there. But... what do I know?
1287. RitaEvac
1286. OracleDeAtlantis
Any speculation here, as to what, if say ... he redeveloped in any significant way?
My guess is that it would dissolve the ULL sitting off the East Coast, but that's as far as my mind takes it.
1285. Bobbyweather
1284. CybrTeddy
Actually from what we have seen the overall pattern favors landfalls, ie Isaac, Ernesto, ect. Suspect we will see another system like that before years out. This is due the abundance of dry air in the Atlantic, causing storms to go more westward.
1283. VR46L
1282. Patrap
Ahh, a Chuck Berry tune.
1281. AussieStorm
I'm very much looking forward to our upcoming summer. bring on the 100+ days. I love them. Not had them in since summer 2009.
1280. jeffs713
Nadine
1276. Tazmanian
Yep
1273. CybrTeddy
Didnt see that, so yup, we have TS Michael.
1272. jeffs713
That looks like sleet. (please send some to North America... I'm done with summer)