91L near tropical depression status

By: Dr. Jeff Masters , 2:08 PM GMT on August 02, 2010

Share this Blog
2
+

A tropical wave near 12N 41W, midway between Africa and the Lesser Antilles Islands, is very close to being a tropical depression. NHC labeled this system Invest 91L yesterday, and is giving it a 90% chance of developing into a tropical depression by 8am Wednesday. Wind shear is a low 5 - 10 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of 91L to potentially allow further development. The main negative for development appears to be the storm's small size, which makes it vulnerable to modest increases in wind shear or dry air entrainment. A Windsat pass from 5am EDT this morning did not show a closed circulation. Satellite imagery shows that the intensity and areal extent of 91L's heavy thunderstorms is very limited, but that a closed surface circulation may be close to forming. Low-level spiral bands and upper-level outflow are not apparent yet.


Figure 1. Morning satellite image of Invest 91L.

Forecast for 91L
There is modest model support for 91L developing into a tropical depression. Three out of six of our reliable models for forecasting tropical cyclone genesis predict 91L will develop into a tropical depression by Tuesday or Wednesday. A west-northwest motion at 10 -15 mph is predicted, which should carry 91L a few hundred miles northeast of the northernmost Lesser Antilles Islands. However, it is possible that 91L would track over the northernmost Lesser Antilles Islands, as predicted by the Canadian model. Squalls from the outer rainbands of 91L may affect islands such as Antigua and Barbuda as early as Wednesday afternoon. As 91L makes its closest approach to the Lesser Antilles on Wednesday, the storm will begin to encounter strong upper-level westerly winds associated with the counter-clockwise flow of air around an upper-level low pressure system centered between Bermuda and Puerto Rico. The latest SHIPS model forecast predicts that these winds will cause wind shear to rise to the moderate level, 10 - 20 knots, by Tuesday night, and to the high level, 20 - 30 knots, by Wednesday. There is also a great deal of dry air associated with the upper level low that may cause problems for 91L. The high wind shear and dry air should weaken and possibly destroy 91L late this week.

A trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough may be strong enough to recurve 91L far enough to the northwest that the storm will threaten Bermuda. The HWRF and ECMWF models predict 91L could pass very near to Bermuda on Saturday. It is uncertain at this time if the trough will be strong enough to recurve 91L all the way out to sea early next week, as predicted by the GFS model, or leave 91L behind to potentially move westward again into the U.S. East Coast, as predicted by the Canadian model. The amount of wind shear that might be present early next week is also highly uncertain.

Cyprus records its hottest temperature in history yesterday
The island of Cyprus recorded its hottest temperature in its history on August 1, 2010 when the mercury hit 46.6°C (115.9°F) at Lefconica. The old record for Cyprus was 44.4°C (111.9°F) at Lefkosia in August 1956. An older record of 46.6°C from July 1888 was reported from Nicosia, but is of questionable reliability.

The year 2010 is now tied with 2007 as the year with the most national extreme heat records--fifteen. There has been one country that has recorded its coldest temperature on record in 2010; see my post last week for a list of the 2010 records. My source for extreme weather records is the excellent book Extreme Weather by Chris Burt. His new updates (not yet published) remove a number of old disputed records. Keep in mind that the matter of determining extreme records is very difficult, and it is often a judgment call as to whether an old record is reliable or not. For example, one of 2007's fifteen extreme hottest temperature records is for the U.S.--the 129°F recorded at Death Valley that year. Most weather record books list 1913 as the year the hottest temperature in the U.S. occurred, when Greenland Ranch in Death Valley hit 134°F. However, as explained in a recent Weatherwise article, that record is questionable, since it occurred during a sandstorm when hot sand may have wedged against the thermometer, artificially inflating the temperature. Mr. Burt's list of 225 countries with extreme heat records includes islands that are not independent countries, such as Puerto Rico and Greenland. Seventy four extreme hottest temperature records have been set in the past ten years (33% of all countries.) For comparison, 14 countries set extreme coldest temperature records over the past ten years (6% of all countries). I thank Mr. Burt and weather record researchers Maximiliano Herrera and Howard Rainford for their assistance identifying this year's new extreme temperature records.

Next update
I'll have an update later today if 91L develops into a TD.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

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

Viewing: 209 - 159

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

IDK, I won't be calling anyone a anything "caster" so long as they aren't totally off the rocker...like saying that TD4 is going to strengthen to a 5 and hit NOLA (that would FOR SURE be a "wish" caster.) I think that saying that the front won't be strong enough, etc. etc. opens up the blog for healthy debate. Since weather isn't an exact science, it takes all view points to eventually learn from or prove/disprove a thesis with data. Even the outlier ones :)
Member Since: Posts: Comments:
Flood - 'morning (or almost afternoo here).

I hope you are correct... or at least this stays a fish storm. However, I will remain ever vigilant at watching. As a "Watched Storm Never Comes".
Member Since: Posts: Comments:
207. IKE
TD4....

Member Since: June 9, 2005 Posts: 23 Comments: 37860

I'm going with the BAMD!



BAM (Beta and Advection) uses vertically-averaged winds and computes trajectories provided by the GFS model to provide track forecasts. There are three forms: BAMD (BAM Deep, 850–200 hPa), BAMM (BAM Medium, 850–400 hPa) and BAMS (BAM Shallow, 850–700 hPa) that use different altitudes of wind.[1] For a weak hurricane without a well-developed eye wall extending deep into the atmosphere (or for a tropical storm), the shallow-version model may work well, because weak storms tend to be steered by low-level winds.[1] As the storm grows stronger and the eye wall gets deeper, the deeper versions become more accurate, as these types of storms are steered more by the winds in the upper-level. If the forecast from the three versions is similar, then the forecaster can conclude that the storm may go as predicted, but if the versions vary by a great deal, then the forecaster has less confidence in the track predicted.[1] Large differences between model predictions can also indicate wind shear in the atmosphere, which could affect the intensity forecast as well.[1]<
Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting XLR8:
OMG!! Someone please turn the oven off, I think I'm done. It is 94 degrees at 10 AM with a heat index of 107 in Flowood, MS. YUCK
Sorry for you, Hot here in Texas also but No humidity so I will take it.
Member Since: Posts: Comments:
It is still a waiting game. Conditions will change each day. Just yesterday all the experts on this blog were saying that shear would be low for the next seven days and that there was nothing out there to stop the development. Today we are hearing the opposite. I have the feeling that NHC is just playing it safe and declaring TD4 at this time even if they are not sure of what is going to happen.
Member Since: August 10, 2009 Posts: 0 Comments: 167
Don't forget the infamous quote, "season is a bust"
Member Since: Posts: Comments:
Quoting weatherwart:
Lightning fried my TV last night, my neighbors chickens are loose in my yard and we have a TD.

This day has started off well. lol

LOL
Member Since: Posts: Comments:
Quoting JupiterFL:


Too bad the lightning didn't fry the chickens.




LOL!
Member Since: Posts: Comments:
Well, if the ECMWF is to be believed, I'll get the rain in about ten days.

Member Since: Posts: Comments:
Quoting stormpetrol:
Call me a "westcaster" but for the past 5-6 hours td#4 has been due west imo.

Westcaster...sorry, you asked for it. :)
Member Since: Posts: Comments:
198. SLU
Updated 2010 storm tracks

Member Since: July 13, 2006 Posts: 13 Comments: 5367
Quoting divdog:
florida caster


Did I say Florida in any part of that statement? I said 4-5 or days from now, I didnt say that after that it would go directly into Florida, So hush your mouth, and leave the blog if your going to attempt to stir the pot.
Member Since: Posts: Comments:
Quoting DestinJeff:


If anything that current track will bring them out even more!

"Trough won't be strong enough..."

"Models tend to shift west"

"High will build back in..."

"Weakness isn't very strong"

etc etc...

"There's dry air ahead of it..."
"It will be moving into an area of high shear..."
Member Since: Posts: Comments:
Quoting weatherwart:
Lightning fried my TV last night, my neighbors chickens are loose in my yard and we have a TD.

This day has started off well. lol


Too bad the lightning didn't fry the chickens.
Member Since: Posts: Comments:
193. IKE
Quoting DestinJeff:


If anything that current track will bring them out even more!

"Trough won't be strong enough..."

"Models tend to shift west"

"High will build back in..."

"Weakness isn't very strong"

etc etc...


LOL!
Member Since: June 9, 2005 Posts: 23 Comments: 37860
ya, as a novice wishcaster itt doesnt seem likely that the storm will hit near me at any significant strength, seems likely it will a)fizzle out to no more than bonnie rainstorm strength or b) head out to sea or c)both, and i wouldn't hold my breath on the one behind it since it should stay strong enough to eat up any energy the next wave would need for good formation, seems like 90L stalled & killed 91L and vice versa so i expect the next one will do the same and have the same done; we just cant get any cool storms here since 05. Katrina was so-so here but Wilma was great but absolutely nothing since for us beach going 24hr max FPL power repairing condo dwelling wishcasters
Member Since: Posts: Comments:
Quoting cirrocumulus:
The east coast front won't make it far enough south to recurve 91L. The temperatures are too warm this summer.
more florida casting
Member Since: Posts: Comments:
Call me a "westcaster" but for the past 5-6 hours td#4 has been due west imo.
Member Since: Posts: Comments:
Quoting cirrocumulus:
The east coast front won't make it far enough south to recurve 91L. The temperatures are too warm this summer.


You mean TD 4.
Member Since: Posts: Comments:
Quoting tropicfreak:


But the dry air is associated with the ULL. It is moving west as well.


From the Docs entry above:

There is also a great deal of dry air associated with the upper level low that may cause problems for 91L. The high wind shear and dry air should weaken and possibly destroy 91L late this week.
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Lightning fried my TV last night, my neighbors chickens are loose in my yard and we have a TD.

This day has started off well. lol
Member Since: Posts: Comments:
Quoting IKE:


Notice how the blog posts have slowed down since the NHC advisory?


yup! i think the track is great if it means it will be pulled out to sea! y would someone be happy that the cone has a system directed for them...i dont want to see wishcasting i want to see good forecasting
Member Since: Posts: Comments:
The east coast front won't make it far enough south to recurve TD4! The temperatures are too warm this summer.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting sammywammybamy:




lol. in other news


Good were in agreement that we have no idea what this system will do intensity wise.
Member Since: Posts: Comments:
Quoting SLU:
Safe to say there's a lot of uncertainty with TD #4.


LMAO...you think?
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Quoting Floodman:


Morning, all..Dak!

Man, this is way too early...but if the forecast shear pans out, it'll be lucky to make TS. It has a number of strikes against it, not the least of which is it's size...add to that the dry air out in front if it:



It's not impossible for it to develop further but the prospects are rather grim...


But the dry air is associated with the ULL. It is moving west as well.
Member Since: Posts: Comments:
Quoting truecajun:


you have to refresh before your comment will show up.


even when i refresh they do not always show up
Member Since: Posts: Comments:
Quoting Neapolitan:


Huh? Ike was complete outside to the left of that cone at the end of the 5 days. About the only thing they got "right" was the temporary southward dip.


12Z on the 9th was at 22.4/82.4, which is pretty close to the SW side of the cone at 5 days.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Fantastic news, track takes it away from gulf and Florida
Member Since: Posts: Comments:
174. SLU
Safe to say there's a lot of uncertainty with TD #4.
Member Since: July 13, 2006 Posts: 13 Comments: 5367
Quoting Dakster:
I notice that the NHC doesn't expect this to get any stronger that a TS, does everyone here agree with this?


Morning, all..Dak!

Man, this is way too early...but if the forecast shear pans out, it'll be lucky to make TS. It has a number of strikes against it, not the least of which is it's size...add to that the dry air out in front if it:



It's not impossible for it to develop further but the prospects are rather grim...
Member Since: August 2, 2006 Posts: 10 Comments: 9922
TD 4!!!! :D

Just got on.
Member Since: Posts: Comments:
171. XLR8
OMG!! Someone please turn the oven off, I think I'm done. It is 94 degrees at 10 AM with a heat index of 107 in Flowood, MS. YUCK
Member Since: Posts: Comments:
As 04L pulls away at a faster speed, the disturbance behind it, if it continues to persist, could be our next best chance for development.
Member Since: Posts: Comments:
169. IKE
Quoting New2SOFLA:
just what i mean.......its crazy that ppl are dissapointed that the cone takes it away from coast.....since the update all im seeing is ppl wishing this storm further west...seems like the carolinas and mid-atl need to watch this more than florida and the gulf....


Notice how the blog posts have slowed down since the NHC advisory?
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting Dakster:
I notice that the NHC doesn't expect this to get any stronger that a TS, does everyone here agree with this?


There intensity forecast are usually on the lower end always. Better to be conservative on the intensity, not trying to freak people out if it never pans out.

Until they see the storm really intensifying quickly why call for a hurricane until it show signs.
Member Since: Posts: Comments:
just what i mean.......its crazy that ppl are dissapointed that the cone takes it away from coast.....since the update all im seeing is ppl wishing this storm further west...seems like the carolinas and mid-atl need to watch this more than florida and the gulf....
Member Since: Posts: Comments:
166. IKE
Quoting DestinJeff:


What are you? New?


I got to thinking that was stupid of me to say that on here.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
From the local met office:

RIGHT NOW IT LOOKS LIKE THE GFS IS TOO AGGRESSIVE WITH
TRYING TO PUSH A WIND SHIFT/FRONT INTO THE REGION FROM THE NORTH BY
SUNDAY...ESPECIALLY GIVEN THE TRACK RECORD OF ANY OTHER FRONTS THIS
SUMMER.


They've been complaining about the models being too aggressive with East Coast fronts all summer long.
Member Since: Posts: Comments:
IT IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.
Member Since: Posts: Comments:
Quoting K8eCane:
Georgia keep an eye peeled


The entire US and Canadian east coast, and even the eastern Gulf Coast needs to pay attention to this storm. However if the 06z GFS pans out then it won't even make landfall at all.
Member Since: Posts: Comments:
Quoting DestinJeff:
Here is some early modeling on Ike, that would have left a safe taste in the mouth of those on the TX coast.



Gotta love a safe taste.
Member Since: Posts: Comments:
Wow.......Dr. M and NHC thinking that sheer might rip it apart in a few days......These things have a mind of their own sometimes....Just have to wait to see how much of a groove it can get in the short term before it hits the sheer.
Member Since: Posts: Comments:

Viewing: 209 - 159

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

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
28 °F
Overcast

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron