Don battling dry air and wind shear
Tropical Storm Don continues to be an unimpressive low-end tropical storm as it continues northwest towards the Texas coast. Don formed yesterday afternoon from an African tropical wave that moved into the Gulf of Mexico under a region of low wind shear. Don's formation date of July 27 is nearly a month ahead of the usual August 23 date for the arrival of the season's fourth named storm of the year. There is currently no hurricane hunter airplane in Don, and a new airplane is not due in the storm until tonight. The last center fix at 1pm EDT found surface winds of 45 mph and a central pressure of 1005 mb, a 4 mb rise from earlier this morning. Water vapor satellite images show a region of dry air to the northwest of Don, over the western Gulf of Mexico. Wind shear as diagnosed by the University of Wisconsin CIMSS group and the SHIPS model show a moderate 5 - 15 knots of shear from strong upper level winds out of the north. This shear is creating problems for Don by injecting dry air into the system. Visible satellite imagery from early this afternoon showed the presence of surface arc-shaped clouds expanding outwards to the north from the center of Don. These type of clouds are a sign that the storm is struggling with dry air. When dry air at middle levels of the atmosphere gets injected into thunderstorms due to wind shear, the dry air tends to create strong downdrafts that rob the storm of moisture. These downdrafts spread out at the ocean surface and create arc-shaped surface cumulus clouds.
Figure 1. Visible satellite image of Don from pm EDT July 28, 2011, showing arc-shaped surface clouds--the tell-tale sign of dry air interfering with the storm's organization.
Figure 2. The latest drought map for Texas shows that over 75% of the state is in exceptional drought--the highest category of drought. Image credit: U.S. Drought Monitor.
Forecast for Don
The big question for Don is, will it bring significant rains to Texas? According to the National Climatic Data Center, the six-month period ending in June 2011 was the driest on record. Average rain between January and June was more than eight inches (203 millimeters) below average in Texas, and the state experienced record heat between April and June. The heat and lack of rain have brought exceptional drought--the highest category of drought--to over 75% of the state. Don has the potential to bring some decent drought-busting rains to the state. If Don can expand in size and intensify to a 50 - 55 mph tropical storm, it has the capability to bring hundreds of millions of dollars worth of beneficial rains to the state. We don't want Don to stay in its current state, which is too small and weak to bring significant rains to Texas. If Don follows the current NHC forecast, which brings the storm up to a moderate-strength tropical storm, that would be just right. Don's small size makes it prone to dry air and wind shear, though, and it is uncertain whether the storm can overcome these problems enough to become a significant rain maker. NHC gave Don a 12% chance of intensifying into a hurricane in the 11am advisory, which is a reasonable forecast, since Don is running out of time to get its act together in time to become a hurricane. None of the computer models is predicting Don will become a hurricane.
For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast. The 11 am version of this forecast shows that Port O'Connor, Texas has the highest chance of tropical storm-force winds (39+ mph): 45%.
New hurricane archive search feature
The autocomplete entities in the wunderground search box has been extended to include hurricanes, so you can now search for a storm by name, year, or basin. Here are some examples in case you feel like exploring your new options:
By name:
Hurricane David - Atlantic, 1979
David, Major Hurricane - Atlantic, 1979
Major Hurricane David - Atlantic, 1979
By year:
2005 Hurricanes Atlantic
2007 Hurricanes Eastern Pacific
By basin:
Hurricanes Western Pacific 2011
Hurricanes Atlantic 2008
By category:
Tropical Storms Atlantic 2005
Tropical Depressions Indian Ocean 2011
Subtropical Storms Eastern Pacific 2010
Extratropical Storms Western Pacific 1988
I'll have a new post Friday morning.
Jeff Masters
Reader Comments
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Taco :o)
Also, looking at the broad nature of 91L, I think most of the models are over cooking it in intensity as it is still way off from TD status...
Expect the models to shift a little WEST as the forecast intensity come down... it already has with SHIPS showing 125mph earlier and now 85 mph at best..
Let the fun begin.. :)
Don - Vortex run to STBD of track (further north of the US/Mex Border) with a 1004 reading
91L - Multiple Models have it becoming a CAT 3-4 system into the Windward Isles
TS BUSTED FORECAST ALIBI
YES........looks like a MAJOR and i BIG MAJOR....this is a giant turning tons of atmosphere.......i mean a bunch too.
Let the East Coast drama begin.
Taco my friend.......i feel ya! When in Neutral ESNO conditions.......this is what we get. Many forget that i think. Shear had been running below average in the Atlantic Basin most of spring....its carrying over now.
Some giant wave again!
Sorry, but I don't buy into the "hypercane" crap. Sounds like some science fiction/natural disaster fanatic trying to create a new storm that any weather weenie would love to see develop just to scare people.
500mph winds over water temperatures of 50C? Right...
1-don
2-91L3
wave behind 91L with a spin l0l
4- blob in the caribiean
all eyes on 91l for now but could the others form also? busy week ahead get all your tracking tools out and lots of coffee
Maybe still possible? or not? or possible? or-AH FORGET IT
I very much know this and there will be a lot of pepole in here will not like having to deal with "FEMA" (which as no "MONEY") and there insurance company leaving Town....
Tampa I know I donot like this setup as it is right now....
Taco :o)
Cutoff low... we only get about one of those every other year...
computer models are only as good as the variables that are put in them. Dry air, wind shear, trough, high pressure, water temps, steering currents, jet stream, etc....
If any one of these changes, the track could change.
best conclusion is stay tuned
91L is going thur the same environment as Don did, it took Don a while to develop so maybe it will take 91L a while too.
My sense on the Euro is that it hasn't been on board with anything once a system has a low pressure center. It'll develop vort area's and then drop them when they get more organized - been kinda weird from my perspective
TACO!...not liking 91L at all...this one looks like it is gonna be an east coaster all the way...watching to see how close to PR it comes in the next 5 days... and to beat all...it puts it about 10-15 days out if it is an east coaster...and school starts here Aug 18...yay...just in time to delay school...woo hoo
the only possible way a hypercane can form is if a meteor hits the ocean.... BBOOOOMM hypercane but thatss the only way im awareit can happen
not saying it could/would happen....but wonder what would happen if a large hurricane was striking land just as a quake happened under water...what would the surge do...ugly thoughts just came to mind....
YEPPERS.........you are so correct!
i wonder what the state of louisiana would look like after this happened..... archepeligo here we come
Puerto Rico, Bahamas, and South Florida might be in for a doozy with 91L.........i don't like this at all.
Link
actually was thinking of east coast...Awendaw (just n of Charleston, SC) had a surge that was unbelieveable...people in 2 story houses had to get on their roofs because the second floor wasn't high enuf...
And Good Morning to you too while I'm having my 3rd cup of coffee....
Setup not looking good at all :o)
Taco :o)
Hey Tampa...how goes it? IMO not just FL...it will depend where around PR it hits and how weak/strong the trof is...not liking it at all...this one could be a sweeper and nail the whole east coast
I noticed the other day the water temperatures from Miami east south east along the Islands down to Virgin Islands, that area to the north of that line is all above 85+ and is much above normal. It has really warmed up in that belt over the last week.
What is shear looking like for the future of 91-L?
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