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

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 37 - 1

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 — Blog Index

Quoting 7544:


yeap its looking good at this hour and with the hot waters in gulf hmmmmm can he be reborn afterall when will he get it in the gulf maybe tomorow ?



It will be totally out over the GOM by tomorrow morning. As far as the ULL over the Bahamas, it will all depend upon how close they get to each other.
Member Since: December 31, 1969 Posts: Comments:
Quoting RTSplayer:
No argument about the meaning of HSI. However, local storm surge, rainfall, total duration, maximum wind, etc. are the items that go into a personal decision to prepare and/or evacuate. All of those items are already forecast without resorting to another index. Widespread damage highlighted by HSI potential may be interesting, but it does not drive evacuations. Actually, quite the opposite. It makes evacuation more difficult. Likewise, the potential for widespread power loss does not really drive anyone to evacuate.

Your point appears to be one of finding a scheme to help *individuals* make better decisions in advance of a storm. If so, concentrate on *individual* factors and forget about the billions of dollars in total damage.

One of the more common reactions quoted over the past week has been, "We didn't think it would be this bad." Even though the forecasts called for up to 20 inches of rain over a large area, many folks were apparently basing their expectations on past experience rather than current forecasts.


The record wide spread flood in Louisiana was actually a spring storm in 1983, and for hte north side of most parishes it's records remain.

The Isaac forecasts were flawed regarding inland flooding and storm surge because of two basic reasons.


1, The size was most certainly not properly understood for forecasting storm surge and river and bayou backups due to prolonged winds out of the south and east. Killian, Louisiana broke their previous flood record by around 7 or 8 feet, and yellow Water Creek in Tangipahoa parish south of Highway 22 broke it's previous record by around 4 or 5 feet.

2, The changes in drainage since 1983 spring flooding were not taken into consideration, and the 1983 flood did not involve a storm surge, but just enormous rainfalls. The improvements on highway 190 and Interstate 12 allowed upstream waters to flow downstream far faster than they did in 1983, sparing the north sides of most parishes the insane "daming" effect that caused outrageous water levels there. However, since this water got downstream faster, it combined with the above normal storm surge at the mouths of bayous and rivers, and contributed to smashing flood records in some streams and rivers on the south side of the parish.

The only way to fix this is to install a massive flood gate between Lakes Pontchartrain and Maurepas, to keep the lake level low enough to allow the rivers to drain, as a levee around Maurepas will help SOME but will not stop water being backed up in the mouths of the rivers anyway.

However, if you do THAT, then Pontchartrain will be a foot or two higher, which will slow down the drainage of Tangipahoa river and other rivers east of Lake Maurepas.


I hate to say it, but they may need to plug back up a bridge or two, or a culvert or two on 190 and I-12, so as to split the difference back to the north side of the roads and give the lower parts of the basins more time to drain in a hurricane situation.



I kid you not, if Isaac had been a large Cat 2 instead of a large cat 1, I would have taken several feet of water where I am, and that was "supposed to be" impossible according to flood maps. We aren't even in an evacuation zone for anything less than Cat 5, and we probably would have drowned had Isaac been a large cat 2...Certainly several hundred to perhaps several thousand people in the area would have drowned.


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

Agree or not????
Just a few more thoughts
Member Since: Posts: Comments:
Quoting TomballTXPride:

But no need to worry about 15 days out since patterns will likely change immensely in two weeks. Let's focus on today and even next week first Bud.


Hydrus is free to post long range models and you are free not to look at them, "bud". We don't all "worry" but we are here to talk about weather and all the future possibilities.
Member Since: Posts: Comments:
34. 7544
Quoting GetReal:



It almost looks like a feeder band forming in the north central GOM from the mouth of the Mississippi River, northeast towards NW Florida...


yeap its looking good at this hour and with the hot waters in gulf hmmmmm can he be reborn afterall when will he get it in the gulf maybe tomorow ?
Member Since: Posts: Comments:
Quoting weathermanwannabe:


I hear you. Issac was actually enough as far as impacts and lives lost....A high grade slow moving TS can do more damage than a fast moving Cat 1-2. I am sorry for you loss; I suffered similar impacts (house flooding) from TS Allison a few years back and was lucky that the flood insurance adjuster did not haggle with us and wrote a nice check.

I was referring to the usual number of majors we normally get in a year (I think 2-3 were forecast this year) and the fact that fast speeds (20mph plus at times), dry air, and current sheer issues have keep the majority of the storms in check at TS levels. Goes to show that no one can exactly predict what will happen in any given year because of all of the potential, and sometimes unexpected, "x" factors.


Thanks very much. Oh I knew that you were refering to the lack of "all ducks in a row majors" i.e. winds, pressures, etc. from following your posts.I've been here a while even before I signed up. I just hope for the entire world that we can gain knowledge about what and how these storms are intensifying under the radar so to speak...they getting real sneaky LOL.
Member Since: Posts: Comments:
No argument about the meaning of HSI. However, local storm surge, rainfall, total duration, maximum wind, etc. are the items that go into a personal decision to prepare and/or evacuate. All of those items are already forecast without resorting to another index. Widespread damage highlighted by HSI potential may be interesting, but it does not drive evacuations. Actually, quite the opposite. It makes evacuation more difficult. Likewise, the potential for widespread power loss does not really drive anyone to evacuate.

Your point appears to be one of finding a scheme to help *individuals* make better decisions in advance of a storm. If so, concentrate on *individual* factors and forget about the billions of dollars in total damage.

One of the more common reactions quoted over the past week has been, "We didn't think it would be this bad." Even though the forecasts called for up to 20 inches of rain over a large area, many folks were apparently basing their expectations on past experience rather than current forecasts.


The record wide spread flood in Louisiana was actually a spring storm in 1983, and for hte north side of most parishes it's records remain.

The Isaac forecasts were flawed regarding inland flooding and storm surge because of two basic reasons.


1, The size was most certainly not properly understood for forecasting storm surge and river and bayou backups due to prolonged winds out of the south and east. Killian, Louisiana broke their previous flood record by around 7 or 8 feet, and yellow Water Creek in Tangipahoa parish south of Highway 22 broke it's previous record by around 4 or 5 feet.

2, The changes in drainage since 1983 spring flooding were not taken into consideration, and the 1983 flood did not involve a storm surge, but just enormous rainfalls. The improvements on highway 190 and Interstate 12 allowed upstream waters to flow downstream far faster than they did in 1983, sparing the north sides of most parishes the insane "daming" effect that caused outrageous water levels there. However, since this water got downstream faster, it combined with the above normal storm surge at the mouths of bayous and rivers, and contributed to smashing flood records in some streams and rivers on the south side of the parish.

The only way to fix this is to install a massive flood gate between Lakes Pontchartrain and Maurepas, to keep the lake level low enough to allow the rivers to drain, as a levee around Maurepas will help SOME but will not stop water being backed up in the mouths of the rivers anyway.

However, if you do THAT, then Pontchartrain will be a foot or two higher, which will slow down the drainage of Tangipahoa river and other rivers east of Lake Maurepas.


I hate to say it, but they may need to plug back up a bridge or two, or a culvert or two on 190 and I-12, so as to split the difference back to the north side of the roads and give the lower parts of the basins more time to drain in a hurricane situation.



I kid you not, if Isaac had been a large Cat 2 instead of a large cat 1, I would have taken several feet of water where I am, and that was "supposed to be" impossible according to flood maps. We aren't even in an evacuation zone for anything less than Cat 5, and we probably would have drowned had Isaac been a large cat 2...Certainly several hundred to perhaps several thousand people in the area would have drowned.
Member Since: December 31, 1969 Posts: Comments:



It almost looks like a feeder band forming in the north central GOM from the mouth of the Mississippi River, northeast towards NW Florida...
Member Since: December 31, 1969 Posts: Comments:
Quoting StormPro:

I truely understand the "Official" definition of a Major but if you measure it in lives affected, dollar amounts of damage and shear impacts ol Isaac is in that catagory...18" water in my house from the surge that was feet above forcast, 2 vehicles totalled that should never have gotten wet, and I'm one of the lucky ones.


IMHO, terms such as "Major", "Lower than Average Season" or "Quiet Season" etc are all relative terms best used in "official analyses". All it takes is to get hit by one "Major" or lesser (we have all seen the devastation and fatalities that so-called "Minors" can cause) - to turn a "Quiet Season" into a bad season or, adversely, no hits in a "Busy Season" and a person can feel happier.
A very subjective attitude, I know - but living in Hurricane Alley it is sometimes difficult to be totally objective
Member Since: Posts: Comments:
28. 7544
if isaac gets it in the gulf and heads sse how will the ull by fl effect him will it pull him further south? tia
Member Since: Posts: Comments:
Quoting StormPro:

I truely understand the "Official" definition of a Major but if you measure it in lives affected, dollar amounts of damage and shear impacts ol Isaac is in that catagory...18" water in my house from the surge that was feet above forcast, 2 vehicles totalled that should never have gotten wet, and I'm one of the lucky ones.


I hear you. Issac was actually enough as far as impacts and lives lost....A high grade slow moving TS can do more damage than a fast moving Cat 1-2. I am sorry for you loss; I suffered similar impacts (house flooding) from TS Allison a few years back and was lucky that the flood insurance adjuster did not haggle with us and wrote a nice check.

I was referring to the usual number of majors we normally get in a year (I think 2-3 were forecast this year) and the fact that fast speeds (20mph plus at times), dry air, and current sheer issues have keep the majority of the storms in check at TS levels. Goes to show that no one can exactly predict what will happen in any given year because of all of the potential, and sometimes unexpected, "x" factors.
Member Since: Posts: Comments:
Quoting TomballTXPride:

But it becomes less interesting once we open up your link and find out it's 15 days out. Relax bud.
I am relaxed..The long range shows what pattern may exist whether a storm forms or not..I was not implying that anyone was in danger.
Member Since: Posts: Comments:
Quoting TomballTXPride:
I thought AGW initially meant more storms. Then I remember recently it's been changed to reflect fewer storms but stronger ones?? Where have all the majors been this year. Okay now I'm confused!!!!!!!!

I have a theory....that the climate changing some has affected tropical systems in that they are larger, deeper and more devistating than the "Scale" can acurately measure and much more difficult for our mets to forcast....
Member Since: Posts: Comments:
Quoting jascott1967:


East of Texas/OK year of precip.

Know East Texas is officially out of drought conditions but not for long. Conroe south to Galveston has seen nary a drop of rain for nearly 2 months and hot, hot, hot. 100's all week is the forecast.


Same here in Lubbock. No rain since some thunderstorms a couple of weeks back and still around 100F!

Not really complaining about the heat though..... will not be long before the frosts come and that will be the end of the vegies!
Member Since: Posts: Comments:
12Z NAM 84 hrs Ex Isaac near west coast of FL

Member Since: Posts: Comments:
Next week will be more interesting
Member Since: Posts: Comments:
Another view of a possible significant development for our part of the world..A bit concerning when one takes a close look....Here is the run....Link
Member Since: Posts: Comments:



LESLIE
11:00 AM AST Tue Sep 4
Location: 25.0N 62.5W
Moving: N at 3 mph
Min pressure: 994 mb
Max sustained: 65 mph
Member Since: Posts: Comments:
Quoting Grothar:
Link of disturbed weather in the Southeast.


Link


East of Texas/OK year of precip.

Know East Texas is officially out of drought conditions but not for long. Conroe south to Galveston has seen nary a drop of rain for nearly 2 months and hot, hot, hot. 100's all week is the forecast.
Member Since: Posts: Comments:
Quoting weathermanwannabe:
Thank You Dr. Very weird year so far with high numbers and no majors yet going into the peak.

I truely understand the "Official" definition of a Major but if you measure it in lives affected, dollar amounts of damage and shear impacts ol Isaac is in that catagory...18" water in my house from the surge that was feet above forcast, 2 vehicles totalled that should never have gotten wet, and I'm one of the lucky ones.
Member Since: Posts: Comments:
Thank you Dr. Masters
Member Since: Posts: Comments:
I predict a slow blog week.
Member Since: Posts: Comments:
Here's an easy system.

1, Start with 1015mb.

2, Find the approximate area covered by each full Millibar of pressure in square kilometers, but not overlapping stronger(lower) pressure values. i.e. the area of each amorphous "donut" of pressure lines around the CoC.

3, For each partition, subtract forecasted landfall intensity in pressure from 1015.

4, Square the result of the pressure subtraction for each partition and multiply by that partition's size.

5, Add all of the partitions.

6, Do the same for historical storms.

7, Compare the results of the forecast to actual values of other real hurricanes.


This would solve both the size and intensity issues by combining them in a multiplicative index directly related to size and pressure.

The initial values would be very large, but could be scaled down and formatted to manageable numbers by simply dropping the last N digits.

Then you would compare analog landfalls in the public broadcast.

This would give an exact, scientific value to the instantaneous severity of the forecast landfall, rather than "guesswork" on vague notions of size and wind speed.

In this system, a 940mb ring would be given 33% more points than a 950mb ring of the same size.

The score would be expressed in "scientific" units of (mb^2)*(km^2), which has an absolute meaning, rather than vague concepts, and is similar to the IKE value, except it represents an instantaneous severity.


ACE is truly useless for forecasting, and is only useful for ranking a storm after the fact.

Systems like HSI or the one I just made up on the spot, would be excellent as forecasting tools, because they can be predicted within certain margins of error, and they can be related to instantaneous destructive potential, rather than cumulative effects over long times (which truly are meaningless in most cases since most ACE is aquired out over the open water where it effects almost nothing..)
Member Since: December 31, 1969 Posts: Comments:
Link of disturbed weather in the Southeast.


Link
Member Since: December 31, 1969 Posts: Comments:
Thank you Dr. Masters
Member Since: Posts: Comments:
Thanks for the update, Doc. Any thoughts when the large anti-cyclone is to build over Leslie?

Member Since: December 31, 1969 Posts: Comments:



Low level clouds across the GOM are already beginning to flow into the remains of Isaac. He should not have much problem spinning back up once over the GOM. IMO


Link
Member Since: December 31, 1969 Posts: Comments:
THanks for another great update Doc. The tropics are really kicking into gear as we head into the peak of the season. How are all of the bloggers today?
Member Since: Posts: Comments:
Thank You Dr. Very weird year so far with high numbers and no majors yet going into the peak.
Member Since: Posts: Comments:
thanks.dr.masters.no.isacc.info?
Member Since: Posts: Comments:
Thanks, Doctor Masters. I'm home sick today... -__-
Member Since: December 31, 1969 Posts: Comments:
had a long weekend away.. a few developments, thanks for the update Doc!
Member Since: Posts: Comments:

Viewing: 37 - 1

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 — Blog Index

Top of Page

Category 6™

About

Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather