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
Leslie headed towards Bermuda; Tropical Storm Michael forms
By: Dr. Jeff Masters , 3:01 PM GMT on September 04, 2012
Tropical Storm Leslie continues to suffer from 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. Satellite loops show that Leslie has almost no heavy thunderstorm activity near its center, and the storm is crawling north at walking pace, 3 mph. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification. 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 Thursday afternoon. At that time, Leslie will be over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification. However, Leslie's motion will continue to be slow, keeping the storm over its cool water wake, and keeping any intensification slow. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Sunday morning, as indicated in the official NHC forecast. Steering currents for Leslie are expected to be weak through Friday, as Leslie is stuck between two upper level lows. The latest guidance from our top computer models continues to show Leslie making a very close pass by Bermuda on Saturday. 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 48-hour period of tropical storm-force winds beginning Friday night that lasts until Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, but the uncertainty in 4-day NHC forecasts is around 200 miles. Thus, the latest 11 am EDT NHC wind probability forecast calls for just a 12% chance of hurricane force winds on Bermuda on Saturday. Nevertheless, Leslie is 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. 
Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center has very little in the way of heavy thunderstorms surrounding it, thanks to strong northwest winds creating 15 - 20 knots of wind shear.
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 Nova Scotia or Newfoundland, 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 storm may also miss land entirely, and brush by the coasts of Nova Scotia and Newfoundland. Large swells from Leslie reached Cape Hatteras, North Carolina last night, and will begin pounding the entire Eastern Seaboard today through Sunday. These waves will be capable of causing significant beach erosion and dangerous rip currents. The Hurricane Hunters are scheduled to make their first flight into Leslie on Wednesday afternoon.
Figure 2. Morning satellite image of Tropical Storm Michael.
Tropical Storm Michael forms in the Central Atlantic
Tropical Storm Michael has formed in the Central Atlantic on Monday, but is not destined for fame. Satellite loops show that this is a very small tropical cyclone, and the storm is well away from any land areas. Michael is under moderately high shear of 15 - 20 knots, and this shear is forecast to remain at 15 - 20 knots through Wednesday. Since Michael is such a small storm, just a modest increase in shear could destroy it. But if Michael survives until Thursday, when shear is expected to fall to the low range, it has the opportunity to strengthen.
Michaels's formation on September 4 puts 2012 in third place for earliest formation date of the season's thirteenth storm. The record is held jointly by 2005, which had Hurricane Maria form on September 2, and 2011, which had Tropical Storm Lee form on September 2 (there was an unnamed tropical storm that year before Lee.) None of the models show that Michael will threaten any land areas. Michael is a classic example of the type of storm that likely would have been missed before the advent of satellites, since the storm is small, far from land, and may be short-lived.
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™
487. LargoFl
486. Bluestorm5
485. CCkid00
it is moving towards Florida, right?
484. LostTomorrows
This could be very bad news.
And Michael is doing precisely what I thought he would; the same as Chris, Gordon, and Kirk before him... it seems the northerly storms always tend to do really well. There's less dry air further north, and the warmer SSTs definitely extend further and further north each year, it seems. I'm guessing he will continue the trend of hurricanes far north of the MDR.
483. redwagon
Ain't nothing gettin past TX's atmosphere.
482. GTcooliebai
481. LargoFl
480. LargoFl
479. GTcooliebai
478. RTSplayer
model raw / adjusted
12z Euro 939mb / 937mb
The others all ended up in the 965mb range if I remember correctly, so at least the Euro is moving more in line with the consensus or average of the other 3 best models....
477. LargoFl
476. barbamz
Lol. I know a bunch of Michaels (probably like everyone). Takes time to think of all of them whenever the storm is mentioned here.
475. Articuno
Bcuz he's weird xD
JK
474. CCkid00
is this the remnant of isaac?
473. washingtonian115
472. ncstorm
I spy...
471. LargoFl
470. icmoore
Did someone say Bud Light? :)
469. OrchidGrower
Yeah, Cape Coral here so only about 6 miles from Gulf as the crow flies, if that much. Been seein' beautiful t-storms last couple afternoons far to the south, maybe down around Marco, and sometimes in the interior, but nothin' over me. Grass started drying up again yesterday.... :-(
468. RTSplayer
The surge was measured above sea level...
The surge at Waveland and Biloxi broke Camille's records by several feet, and may have been higher than official numbers, but NHC threw out one of the buoy readings near Waveland.
Costliest U.S. Atlantic hurricanes
Cost refers to total estimated property damage
Rank Hurricane Season Damages
1 Katrina 2005 $108 billion
2 Ike 2008 $29.5 billion
3 Andrew 1992 $26.5 billion
4 Wilma 2005 $20.6 billion
Even if you inflation adjust Andrew's damage, Katrina still beats it by a factor of about 2.5...after hitting LESS populated areas...
467. RitaEvac
466. LargoFl
465. Articuno
What's that spin in the central-south GOM?
464. Tropicsweatherpr
Link
463. washingtonian115
462. TropicalAnalystwx13
What does a phoenix have to do with anything?
461. CCkid00
can you post a link please? thanks!
460. GTcooliebai
ISABEL Graphics Archive
459. hurricanewatcher61
458. ncstorm
yeah, lets hope not!
456. Articuno
NO
455. ncstorm
maybe I am reading too much into this but this trough is supposed to be strong and pull Leslie to the north..I have seen "weak".."faster" and "low confidence" in two discussions about this trough..lets hope the models dont do a windshield wiper effect..
454. islander101010
453. GTcooliebai
452. RitaEvac
451. Bluestorm5
450. GetReal
Blob formerly known as Isaac is moving rather quickly south back into N. GOM.
449. leftlink
So... why did the NHC do that, and are the people who did that still in charge of the NHC?
448. OrchidGrower
Geesh, we just left a drought when Deb got here; do we hafta go back to drought already?!
447. GTcooliebai
446. Articuno
MICHEAL MUST SHRINK!
445. TropicalAnalystwx13
Tropical Storm Michael's tropical storm force winds extend out 35 miles from the center of the storm.
Ooh..
444. Dakster
Isn't that what is usually posted prior to the storm track changing to your location.
443. GTcooliebai
442. PalmBeachWeather
441. gordydunnot
440. Articuno
Actually, it was 125mph Category 3.
Actually during it's landfall near Buras-Triumph, it was a Cat 4 with winds I believe of 140 mph.
439. PensacolaDoug
Hope itt doesnt go Humberto on us!
438. ncstorm
THE FINAL
AFTERNOON ISSUANCE PREFERS A LAGGED-AVERAGE APPROACH WHICH USES 30
PERCENT EACH 00Z GFS/ECMWF AND 20 PERCENT EACH 12Z
GFS/ECMWF...WHICH OFFERS A BALANCE OF CONTINUITY...NUDGING TOWARD
THE LATEST GUIDANCE...AND HIGHER MAINTAINING AMPLITUDE. AS SHOULD
BE EXPECTED...CONFIDENCE IS BELOW AVERAGE. THE FINAL RESULT
PRODUCES A PROGRESSIVE LONGWAVE TROUGH OVER THE NORTHWEST AROUND
DAYS 6-7/MON-TUE...AND A WEAKER/FASTER CLOSED LOW TRAVERSING THE
EAST COAST DAYS 5-7 COMPARED TO EARLIER ISSUANCES. GIVEN THAT THE
ANTICIPATED PATTERN APPEARS UNRESOLVED...FUTURE SOLUTION CHANGES
ARE ANTICIPATED...WHICH MAY SUPPORT ADDITIONAL CHANGES TO THE
MEDIUM RANGE PERIOD FORECAST OVER THE NEXT COUPLE DAYS.
437. taistelutipu
Kirk making a re-appearance in a cloaked cling on vessel? The cloaked cyclone, you read it here first!