Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT on July 28, 2011

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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

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I guess it is possible the trough could play a factor with 91L and it's track but as is always with a system that has not even formed yet, it is way too early.

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
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Quoting jasonweatherman2011:
Long term /Monday through Thursday/...
as of 3 am Friday...slightly unsettled weather may remain in place
on Monday as upper troughiness continues in the east while the ridge
builds out west. As the trough moves off the coast on Tuesday
northerly flow continues aloft but the cyclonic curvature fades away
and rainfall chances diminish accordingly. This setup will remain in
place for the rest of the long term. Rain chances will be quite
minimal but at least temperatures will be seasonable. There is some
interesting agreement in models showing a piece of the trough
splitting off and trying to develop low pressure in the Bahamas near
or just beyond the end of the long term. Its getting to be that time
of year.

new storm on east coast!!


Cutoff low... we only get about one of those every other year...
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Quoting TampaSpin:


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.


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)
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2318. GHOSTY1
If that is a turn to the NNW i think landfall a little south of CC isn't of the question, but i gotta go and will be back later.
Member Since: July 25, 2011 Posts: 0 Comments: 453
Quoting weatherman566:


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...


Maybe still possible? or not? or possible? or-AH FORGET IT
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2316. 7544
morning all looks like we have 4 on watches this am

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

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2314. GHOSTY1
Hey guys i can only be on for a second but i was looking at dons rainbow imagery and did he take a turn to the NNW? Toward the last few frames
Member Since: July 25, 2011 Posts: 0 Comments: 453
Hey all. What's the latest on TS Don?
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Quoting Vincent4989:

Wait... it should happen in 2030 or so on NOT NOW.


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...

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Quoting jasonweatherman2011:
what is going on in the caribbean

Some giant wave again!
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Quoting hurricanehunter27:
G cat7 hypercane.
F
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Quoting taco2me61:
Ok so if 91L is named in 24hrs we will have our 5th named storm in July which could be another year like 2005.... And I donot like it at all....

Taco :o)


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.
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2307. Walshy
Quoting Walshy:
National Weather Service Wilmington NC

There is some interesting agreement in models showing a piece of the trough splitting off and trying to develop low pressure in the Bahamas near or just beyond the end of the long term. Its getting to be that time of year.

Link


Let the East Coast drama begin.
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2305. WoodyFL
36 hours pressure



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Quoting stillwaiting:
,more than likely our first hurricane of the yr,looks like Emmy could become a major imo



YES........looks like a MAJOR and i BIG MAJOR....this is a giant turning tons of atmosphere.......i mean a bunch too.
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Complete Update

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





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2302. NASA101
One major model is not on board is the European - would like to some consensus from ECMWF - as currently it just shows a wave going through the Caribbean!

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.. :)
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Ok so if 91L is named in 24hrs we will have our 5th named storm in July which could be another year like 2005.... And I donot like it at all....

Taco :o)
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Quoting hurricanehunter27:
G cat7 hypercane.

Wait... it should happen in 2030 or so on NOT NOW.
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Quoting TampaSpin:



The forecast models are not playing around with 91L........OUCH
,more than likely our first hurricane of the yr,looks like Emmy could become a major imo
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I currently have 5 Floaters up on Don........i can put the same 5 Floaters up on 91L.....but i am afraid it will drag some of your computers down.......WHat imagery is the most important for you all?
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91l center fix,10N,43W imo
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models have shifted to the north, maybe in response to a trough. this maybe as a result of the models have it get strong too quickly
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Quoting hurricaneben:
POLL: How strong will 91L be at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5
G cat7 hypercane.
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2292. WoodyFL
caribbean view




91L

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Quoting jasonweatherman2011:
the trough is much weaker now and moving out faster now where is the trough now i do not see it anymore!!

once again like i said yesterday, NOT A FISH STORM it will NEVER be a fish strom. it will hit the islands and if the trough lifts out, it will get steered wnw towards the east coast. too far out to tell
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting CybrTeddy:


91L is much different than the wave that became Don. 91L is much more organized than that wave, and has a large moisture field with it.


I know he pulled up that monsoon trough with him as he was decoupling from it yesterday. I seen some charts on here showing the water vaper sat pics at different levels of the atmosphere showing some dry air to his northwest, but I have no idea what it looks like today.

30% was a quick bump, just hope the models are over amping this storm. Some ugly scenerios on some of them right now.
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2289. Walshy
National Weather Service Wilmington NC

There is some interesting agreement in models showing a piece of the trough splitting off and trying to develop low pressure in the Bahamas near or just beyond the end of the long term. Its getting to be that time of year.

Link
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Quoting Gearsts:
More north but a weaker system? Dont trust the model runs yet.


I agree with this :o)
It is way too early to even know what it will do or how big the Storm will be :o)

Taco :o)
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2287. Gearsts
Quoting weatherh98:


who cares at this point... f
D
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Quoting hurricaneben:
POLL: How strong will 91L get at peak?

a)Invest
b)TD
c)TS
d)CAT1
e)CAT2
f)CAT3-5


who cares at this point... f
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2283. barbamz

Sort of wave train in the sun, too.
Source: http://spaceweather.com/
Quote from there: Sunspot 1260 is leading a parade of big sunspots across the solar disk--one of the finest displays of solar activity in years. ... Sunspot 1260 has developed a delta-class magnetic field that harbors energy for powerful X-class solar flares.

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2281. nigel20
Good morning everyone. The models showed a similar type track for don. I think we have to wait a couple of days to know the true track of 91l
Member Since: November 6, 2010 Posts: 12 Comments: 8471
Quoting CaneHunter031472:


All I know is that this should be watched closely. We know already where Don is going but this one is not even formed yet. I will be calling my parents in PuertoRico today to let them know of the possibility. You can never be too prepared especially if you have little ones to look after. It would be wise for you to be prepared, not alarmed that's all.
Thanks CaneHunter...i'll definitely be prepared.
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2279. NASA101
Quoting jasonweatherman2011:
i do not know if the trough will turn invesT 91L OUT TO SEA..the trough is much weaker now and moving out faster now


Are you basing your statements on some facts or is it random musings - cannot tell sometimes mate! :)
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The forecast models are not playing around with 91L........OUCH
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Quoting floridaboy14:

well ive got some bad news... the CFS model trys to bring another moderate to strong la nina in the fall which would make the drought even worse..
With La Nina coming back in Texas will have a Dry Fall and Winter is what I am hearing, Texas will get rain but it will be way below what they get normally, kind of the way it has been since last June.
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2275. Gearsts
Quoting jasonweatherman2011:
I SEE THE WINDS ONLY 85 MPH NOW!! WEAKER STORM NOW
More north but a weaker system? Dont trust the model runs yet.
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2274. WoodyFL
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Quoting floridaboy14:


Actually the models have shifted more west.. the HWRF should be excluded for track but if you havent noticed as 91L leaves the carribean the models show it bending back wnw. pay attention to that and the TROUGH thats the key player how strong and how fast it goes



TRUE.. GFS does a good job on picking out the troughs coming down, however the latest 06Z run looks like the trough will be week and high building back in. This has my attention to say the least.
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2272. WoodyFL
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Quoting Skeptic33:


So you're one of many that still believes that saturated fat and cholesterol consumption causes heart disease? That's the mainstream establishment's view yet they are completely wrong when you dig a little deeper in the literature...

Either way, both sides can be wrong.

Another great example - sun causing skin cancer... Dermatologists are screaming at us to avoid the sun and lather on massive amount of sunblock...

What does that do to us? Chronically low vitamin D level leading to significantly higher risk of getting one of 18 different cancers including skin cancer melanoma... multiple types of autoimmune disease, mental disorder, too many to list. Even autism...

So be careful of what you say... Even mainstream establishments can be wrong. Big time.

I haven't kept abreast of the debate about saturated fats, so I can't speak about that with any real depth of knowledge; I just know to limit my intake of them and exercise frequently. However, climate change has been observed through multiple lines of research, and that research has been independently verified multiple times by multiple sources. AGWT/ACCT is solid, and it's real. Now, an industry making hundreds of thousands of dollars in profit every minute of every day won't admit this, but the science is as solid as it gets. To what degree our burning of fossil fuels is contributing is really one of the last unsettled points, but even that appears to be somewhere between "most of it" and "all of it".

We are pumping 40 trillion liters a day of CO2 into the environment. That much of anything doesn't vanish without causing problems.

Anyway: back to the tropics, huh?
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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