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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1071. jdjnola
Quoting CanesfanatUT:


75% of the state is in exceptional drought. Hard to find a spot that doesn't need rain, eh?


Exactly. Besides, most of the moisture will likely fall in the worst parts of the drought even with a landfall due South of CC. (depending on how big Don is).
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Quoting CanesfanatUT:
Can someone give me the NCPS (or something) tropical cyclone info page? It's the one that tracks cyclones formed by the models on each run (0Z, 6Z, etc).

Thanks.


I found it: http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcgen /
Member Since: September 3, 2007 Posts: 0 Comments: 527
1069. Patrap
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1068. jpsb
Quoting bohonkweatherman:
You have wildlife still alive? Most animals around here have been shipped out of state and if they havent they should be. We have no water up here so the so called wildlife does not have a chance, most ponds around here have been dry for at least 2 months.
Here in San Leon, Galveston County we have had 3 rains in the last 8 or 9 months. THREE counting the half inch or so we got today. Ground is like concrete with big cracks in it. Rock hard, I am hoping we will start getting tStorms off the gulf I can see them across the bay (Galveston) but sadly they rarely make it this far west. I had high hopes for Don, seems a perfect storm for us, houston and areas north, oh well, hope this drought ends soon, it's been terrible for 2+ years now.
Member Since: June 30, 2009 Posts: 0 Comments: 1197
Don is very complicated. Always has been -- ever since it was an invest on life support.
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1064. JLPR2
Quoting WeatherNerdPR:

A recent pass showed the CATL AOI's LLC is almost closed, I think.


Yep, it's a little more than halfway there.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
I said last night Don would be a hurricane at landfall, i'm sticking by it 80-90mph one at that, Don is small, but not as small as he might appear! I expect the CATL wave to be labelled 91L tomorrow and there is about 30-40% chance we get a 4th named storm in July!
Member Since: April 29, 2007 Posts: 0 Comments: 8120
1062. Patrap
Quoting MTWX:

Is that fires burning in Mexico??


If you referring to the Radar..Im not sure.
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1061. angiest
Quoting LPStormspotter:
so does that mean it would run along the right side or the other wit arrows


Not sure what it does in that gap. Would seem to allow him room to move further north. But he still has a way to go before he gets in that layer.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting lottotexas:
hope ur wrong

He was wrong before, saying Don would dive SE and die in Hispaniola.
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If Don did undergo RI overnight, that would put him at about 956 or so in the morning. That is what, a cat2 to cat3?
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1058. MTWX
Quoting Patrap:

Is that fires burning in Mexico??
Member Since: July 20, 2009 Posts: 23 Comments: 1393
Quoting JLPR2:
Hello, soon to be 91L.



Ascat on the 40W wave. Center around 8N.
Member Since: September 3, 2007 Posts: 0 Comments: 527
1056. angiest
Quoting lottotexas:
hope ur wrong


Everything else he has said has been wrong.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting Chicklit:
That is one big mass of a tropical wave in the CATL.

Link


Ascat earlier showed the center at around 8N.
Member Since: September 3, 2007 Posts: 0 Comments: 527
Quoting lucreto:
Looks like Don will be headed to Mexico as a 40 mph tropical storm no rains or impacts for Texas.
hope ur wrong
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Quoting HurricaneDean07:
Don has dealt with all of his problems today, and will be in 0 to 5 knots of shear tomorrow, with some dry air tomorrow, though if the dry air is pumped out of its core and it completely closes its core off, then Don will be able to intesify very nicely...

(pre)91L appears to be building a nice anticyclone over it, which will help aid slow development, in addition there is strong cyclonic turning within the tropical wave which will allow it to develop(when/if the time comes)


A recent pass showed the CATL AOI's LLC is almost closed, I think.
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Quoting bohonkweatherman:
You have wildlife still alive? Most animals around here have been shipped out of state and if they havent they should be. We have no water up here so the so called wildlife does not have a chance, most ponds around here have been dry for at least 2 months.


A:"My giant gaping headwound is worse."
B:"No, my giant gaping headwound is worse!"
A:"Mine is!"
B:"Mine!"
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Quoting MiamiHurricanes09:
TAFB at T3.5/65mph.

AL, 04, 201107282345, 10, DVTS, CI, , 2450N, 9100W, , 3, 55, 2, 994, 2, DVRK, , , , , , , , , , , , , , L, TAFB, WB, VI, 5, 3535 /////, , , GOES13, CSC, T, cf=3.0 + 0.5BF= 3.5=DT=PAT=FT.
only 10 miles from hurricane strength, well technically 9... I'm going to go out on a limb and say 80mph Hurricane at landfall
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Can someone give me the NCPS (or something) tropical cyclone info page? It's the one that tracks cyclones formed by the models on each run (0Z, 6Z, etc).

Thanks.
Member Since: September 3, 2007 Posts: 0 Comments: 527
1048. Patrap
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Quoting DisasterResponder:
I humbly apologize for jumping the gun. Does anyone have any crow leftover?


Here you go. You may as well take this bottle of HOT sauce as well. Do not spare the HOT sauce when eating crow. Better to scorch your insides than to taste the crow.
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Quoting angiest:


That's the steering flow for storms 970-989mb. Those are the winds that would guide it. Looks like very little to move it anywhere there.
so does that mean it would run along the right side or the other wit arrows
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Almost looks like a garbage bag being twisted and pulled up from the center.

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105 here today, right now it is clear skies and 96 degrees at 8 pm. I demand Cold Fronts start coming down early this year since Summer started 2 months early. :)
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Don has dealt with all of his problems today, and will be in 0 to 5 knots of shear tomorrow, with some dry air tomorrow, though if the dry air is pumped out of its core and it completely closes its core off, then Don will be able to intesify very nicely...

(pre)91L appears to be building a nice anticyclone over it, which will help aid slow development, in addition there is strong cyclonic turning within the tropical wave which will allow it to develop(when/if the time comes)

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1041. DFWjc
Quoting lucreto:
Looks like Don will be headed to Mexico as a 40 mph tropical storm no rains or impacts for Texas.


Hush! LOL
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Quoting Chicklit:
That is one big mass of a tropical wave in the CATL.

Link


One big mass with a low-level circulation that is almost closed.
Member Since: July 6, 2010 Posts: 113 Comments: 32553
Quoting JrWeathermanFL:
Don lost his 'eye'.


He never had one visible.
Member Since: July 6, 2010 Posts: 113 Comments: 32553
Quoting cctxshirl:


Not true--we need the rain in S. Tx. Wildlife is dying. I think we all need rain equally as bad.
You have wildlife still alive? Most animals around here have been shipped out of state and if they havent they should be. We have no water up here so the so called wildlife does not have a chance, most ponds around here have been dry for at least 2 months.
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That is one big mass of a tropical wave in the CATL.

Link
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Don lost his 'eye'.
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1034. j2008
Quoting WeatherNerdPR:

I agree with them. Don organizing and strengthening nicely this evening.

ATCF has Don at 998 MB and 50 MPH which I think is pretty conservative and low.
Member Since: December 19, 2008 Posts: 1 Comments: 224
1033. Patrap
One should always have a solid Link to declare a invest,, a circle on a Map isnt a Invest..itsa AOI.

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Quoting Gearsts:
New invest? WHERE!?
I think everybody's getting confused, with the yellow circle at 20%. It should be labeled an invest some time tomorrow imo, perhaps even tonight.
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TAFB at T3.5/65mph.

AL, 04, 201107282345, 10, DVTS, CI, , 2450N, 9100W, , 3, 55, 2, 994, 2, DVRK, , , , , , , , , , , , , , L, TAFB, WB, VI, 5, 3535 /////, , , GOES13, CSC, T, cf=3.0 + 0.5BF= 3.5=DT=PAT=FT.
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Just to clear up the misconception, there is no invest currently with the Central Atlantic wave which was mentioned in the 8PM EST TWO.
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Quoting HurricaneDean07:
CI# /Pressure/ Vmax
3.2 / 995.7mb/ 49.0kt


Final T# Adj T# Raw T#
2.9 3.3 3.4

Latest Satellite Estimates from ADT...

So ADT thinks 60 mph 996 MB

I agree with them. Don organizing and strengthening nicely this evening.
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1027. Dirtleg
Someone tell Oz not to park on the beach this time!!!
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1026. Patrap
00z Early Cycle NHC model tracks
Don
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)





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Quoting LPStormspotter:


I'm sorry.. what does that mean?
Thanks for your answer!
If I'm reading the chart correctly it means it would move more farther to the north.
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Quoting HurricaneDean07:
CI# /Pressure/ Vmax
3.2 / 995.7mb/ 49.0kt


Final T# Adj T# Raw T#
2.9 3.3 3.4

Latest Satellite Estimates from ADT...

So ADT thinks 60 mph 996 MB


I agree
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Quoting HurricaneDean07:
Hey everyone!
Im back from my Galveston vacation, and actually heard buzz about Don while I was there...
Hope Don gets stronger, we need the drought buster NOW... 106 today, some small heat showers from Houston to Austin, but not very exceptional in terms of rainfall amounts...

So the latest ive seen is,
Tropical Storm Don:
50 mph
996 MB
moving WNW @ 10

Welcome back. This blog has gotten me very confusd about Don, so I know as much as you. LOL
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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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