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: 759 - 709

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

Levi, If 91L stays just S of the islands, it will avoid strong wind shear, but will it avoid land as it tracks? If it stays weak-- just S of the Islands make since to me.
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
04L/TD/C
MARK
12.6N/41.1W


Looks elongated.
Member Since: Posts: Comments:
04L/TD/C
MARK
12.6N/41.1W NHC LOC
13.1N/42.3W MY LOC
Member Since: July 15, 2006 Posts: 178 Comments: 56018
BWAAHAHAAA

THANK YOU DODA!!!

I was just too lazy to go there m'self...
Member Since: Posts: Comments:
Quoting Levi32:


CMC has something to say these days with regards to track once a system has developed. It was way off with Alex and can be wrong a lot, but once in a while it finds a jewel. We'll see how things turn out.

Yes enough to sustain it but not strengthen. It's on the border of very cold water and that strato-cu field indicates the dry air pressing into the system. Reminds me of the eastern Pacific.


There is no very cold water at all. The SSTs are not the issue, the dry air is And the dry air is not due to the water it is due to the SAL.

Member Since: Posts: Comments:
We need to also keep a careful eye on the disturbance behind 04L.

Member Since: Posts: Comments:
Quoting FloridaTigers:


Wishcasting? :P

CMC is garbage for tracks.


you are incorrect. although the cmc might be known for constantly making cyclones it is also known for how well it handles troughs and ridges and most of the time the cmc is a very reliable mid-range model with regards to track
Member Since: Posts: Comments:
Quoting Snowlover123:


That's not considered ample convection?


Does someone have it out for you? You're always hidden even though I think you post decent (if not at least on topic) stuff
Member Since: Posts: Comments:
Quoting Progster:


its a verb
wishcaster is a noun.


Thank you!!! That bothered me from the previous blog!
Member Since: Posts: Comments:
day 3 in a row of sub-90 degree temps here on the ILM peninsula
Member Since: Posts: Comments:
Quoting DestinJeff:
And now we sit with abated breath, waiting for the 12Z ECMWF.

and, yes, it is "abated" not "bated".


GOTCHA!!!!! LOL

The correct spelling is actually bated breath but it’s so common these days to see it written as baited breath that there’s every chance that it will soon become the usual form, to the disgust of conservative speakers and the confusion of dictionary writers. Examples in newspapers and magazines are legion; this one appeared in the Daily Mirror on 12 April 2003: “She hasn’t responded yet but Michael is waiting with baited breath”.

It’s easy to mock, but there’s a real problem here. Bated and baited sound the same and we no longer use bated (let alone the verb to bate), outside this one set phrase, which has become an idiom. Confusion is almost inevitable. Bated here is a contraction of abated through loss of the unstressed first vowel (a process called aphesis); it means “reduced, lessened, lowered in force”. So bated breath refers to a state in which you almost stop breathing as a result of some strong emotion, such as terror or awe.
Member Since: Posts: Comments:
HWRF 12z has shifted to the left some.
Member Since: Posts: Comments:
Quoting Drakoen:


About 36 hours
thanks
Member Since: Posts: Comments:
Quoting pottery:
MAN!!
We getting the Full Dose here right now, with fireworks added for Special Effect............
Member Since: July 15, 2006 Posts: 178 Comments: 56018
Quoting FloridaTigers:


Wishcasting? :P

CMC is garbage for tracks.


CMC has something to say these days with regards to track once a system has developed. It was way off with Alex and can be wrong a lot, but once in a while it finds a jewel. We'll see how things turn out.
Quoting Drakoen:
TD4 is enough plenty warm water, ample enough to sustain the system. The big problem is the dry air which is limiting convection; however, once the system gets past 50W it will be crossing the 29C isotherm and will have a chance to over come the dry air and really take off.


Yes enough to sustain it but not strengthen. It's on the border of very cold water and that strato-cu field indicates the dry air pressing into the system. Reminds me of the eastern Pacific.
Member Since: Posts: Comments:
Quoting scott39:
how long will that take? I dont feel like doing math right now!LOL


About 36 hours
Member Since: Posts: Comments:
737. Relix
Quoting Drakoen:
TD4 is enough plenty warm water, ample enough to sustain the system. The big problem is the dry air which is limiting convection; however, once the system gets past 50W it will be crossing the 29C isotherm and will have a chance to over come the dry air and really take off.

I kinda have a fuzzy feeling I got that one right and Drakoen verified it. XD
Member Since: Posts: Comments:
Quoting Progster:


its a verb
wishcaster is a noun.


And anal-retentive is an adjective. :-)
Member Since: Posts: Comments:
While the feeder bands have diminshed, the overall convection near the COC has increased, and in the last few frames, you can see new thunderstorms developing.

Member Since: Posts: Comments:
Quoting DaytonaBeachWatcher:


SUCCEEDING DAY OUTLOOK: POSSIBLE NOAA G-IV
SURVEILLANCE MISSION OUT OF TISX AROUND CENTRAL
ATLANTIC SYSTEM FOR 04/0000Z IF IT DEVELOPS.

this might help with that


Good.
Member Since: Posts: Comments:
Quoting Drakoen:
TD4 is enough plenty warm water, ample enough to sustain the system. The big problem is the dry air which is limiting convection; however, once the system gets past 50W it will be crossing the 29C isotherm and will have a chance to over come the dry air and really take off.
how long will that take? I dont feel like doing math right now!LOL
Member Since: Posts: Comments:
732. Vero1

Atlantic Tropical Weather Discussion
--------------------------------------------------------------------------------


000
AXNT20 KNHC 021752
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON AUG 02 2010TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND
RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

TROPICAL DEPRESSION FOUR IS CENTERED NEAR 12.6N 41.1W OR ABOUT
1365 MI...2200 KM E OF THE LESSER ANTILLES AT 1500 UTC MOVING
WNW AT 15 KT. ESTIMATED CENTRAL PRESSURE IS 1006 MB. MAXIMUM
SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT. SEE THE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24
KNHC FOR MORE DETAILS. SOME STRENGTHENING IS FORECAST DURING THE
NEXT 48 HOURS. CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG
CONVECTION ARE FROM 12N-15N BETWEEN 39W-43W.

...TROPICAL WAVES...



Member Since: Posts: Comments:
Quoting StSimonsIslandGAGuy:
As I recall, for hurricane Jeanne, the possibility of a loop was written in the discussions well before it occurred. It was not a total shock.



i also remember,it was forecast by most in the tpa area news as well...
Member Since: Posts: Comments:
MAN!!
We getting the Full Dose here right now, with fireworks added for Special Effect............
Member Since: Posts: Comments:
Quoting gbreezegirl:
Its clouded up here in Gulf Breeze maybe we will get a little. The AC is out at my work!


Hey there, fellow Breezer ;-) I say that, but I live in Pensacola now. Grew up in Gulf Breeze. It stays a few degrees cooler there, you guys are so much closer to the water...although a few degrees in this heat is kind of a drop in the bucket :P
Member Since: Posts: Comments:
Member Since: July 15, 2006 Posts: 178 Comments: 56018
Quoting srada:
Question? Has the CMC been right on ANY tracks this season? I thought it was the ECWMF that has been accurate so why is so many putting so much stock on the CMC taking this into FL?


Wishcasting? :P

CMC is garbage for tracks.
Member Since: Posts: Comments:
Quoting IKE:




That's not considered ample convection?
Member Since: Posts: Comments:
616 leelee75k "Am I mistaken, I recall last week one Dr M's blogs saying that wave behind TD4 would have absorbed it and would be the bigger threat? I guess now that scenario isn't possible or did it happen and I missed it?"

The story was that 91L would eat 90L. 91L did, and grew up to become TD4.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
I think its pretty remarkable that the CMC has TD4/Colin hitting the US in only six days. Thats one heck of a speed demon rolling through the ATL.
Member Since: Posts: Comments:
Quoting angiest:


I'm not entirely sure the models are getting the ridge of the southern US right. While it is not very strong (I am at 1013mb right now) I don't think they have the full extent of it, and as of this weekend it was forecast to spread.


SUCCEEDING DAY OUTLOOK: POSSIBLE NOAA G-IV
SURVEILLANCE MISSION OUT OF TISX AROUND CENTRAL
ATLANTIC SYSTEM FOR 04/0000Z IF IT DEVELOPS.

this might help with that
Member Since: June 29, 2007 Posts: 0 Comments: 1136
Quoting StormChaser81:
CMC 144hrs out, Depicts a storm right on the coast of Miami-Dade county.



It also spins up a nice little storm off the northern coast of South America and moves it into Central America. ;)
Member Since: Posts: Comments:
TD4 is enough plenty warm water, ample enough to sustain the system. The big problem is the dry air which is limiting convection; however, once the system gets past 50W it will be crossing the 29C isotherm and will have a chance to over come the dry air and really take off.
Member Since: Posts: Comments:
Quoting DaytonaBeachWatcher:
Most times you can tell where people are located purely by what they post on here.

Or what their name is, haha :-)
Member Since: Posts: Comments:
Quoting stormwatcherCI:
But then there is the other 30%.
Thats true and you also have to think about how many were in that 30%.
Member Since: Posts: Comments:
Quoting Funkadelic:


When will the 12Z euro be out?
Starts running around 2:30PM EDT and finishes near 3:20PM EDT.
Member Since: Posts: Comments:
717. IKE
Quoting Snowlover123:


What are you talking about? TD 4 has ample convection asscociated with it.


Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting Levi32:
I had the HPC forecast pointed out to me....still showing the ridging directing this into the United States. This isn't a pot-shot recurve yet. My forecast, though not with as much confidence as yesterday, is still for this to impact the United States. We shall see what happens.


I'm not entirely sure the models are getting the ridge of the southern US right. While it is not very strong (I am at 1013mb right now) I don't think they have the full extent of it, and as of this weekend it was forecast to spread.
Member Since: Posts: Comments:
Quoting scott39:
Levi, I saw a video on hurricane season last season, that 70% of waves that develope before or at 40W go out to sea. Have you ever heard of that?


Never heard that particular stat but it's believable. The majority of Cape Verde storms end up recurving. It's hard to get them to come all the way across and make landfall.
Member Since: Posts: Comments:
Quoting StormChaser81:
CMC 144hrs out



CMC is the Florida doom-caster.
Member Since: Posts: Comments:
Quoting jasoniscoolman2010x:
TROPICAL DEPRESSION FOUR WILL BE A WAVE BY TUSEDAY MORNING IF THE T.STORM DO NOT COME BACK TONIGHT..


You trying to emulate STORMTOP or are you living in your basement?
Member Since: June 29, 2007 Posts: 0 Comments: 1136
Quoting jasoniscoolman2010x:
TROPICAL DEPRESSION FOUR WILL BE A WAVE BY TUSEDAY MORNING IF THE T.STORM DO NOT COME BACK TONIGHT..


What are you talking about? TD 4 has ample convection asscociated with it.
Member Since: Posts: Comments:
Quoting scott39:
Levi, I saw a video on hurricane season last season, that 70% of waves that develope before or at 40W go out to sea. Have you ever heard of that?
But then there is the other 30%.
Member Since: Posts: Comments:
710. IKE
Quoting gbreezegirl:
Its clouded up here in Gulf Breeze maybe we will get a little. The AC is out at my work!


That's gotta be rough. Sorry.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting DestinJeff:


although he is in no way a Party of One.
I'm sure that the actual JFV isn't here half of the time that we think he is. I'm almost positive that people come on here, sign up for a username, and then act like they're JFV just to have a little fun.

Back to 04L.
Member Since: Posts: Comments:

Viewing: 759 - 709

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
26 °F
Overcast

JeffMasters's Recent Photos

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