Tropical Storm Don unimpressive so far

By: Dr. Jeff Masters , 2:08 PM GMT on July 28, 2011

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Tropical Storm Don formed yesterday from an African tropical wave that crossed into the Gulf of Mexico, and the thus-far unimpressive storm appears poised to bring tropical storm conditions to the lower Texas coast by Friday night. An Air Force Hurricane Hunter plane arrived in the center of Don around 8am EDT this morning, and has found Don to be a small tropical storm with top winds near 40 mph. The 7:57am EDT center fix found a central pressure of 1002 mb, which is 2 mb higher than NHC was estimating in its 8am EDT advisory. However, a pass through the center at 9:49am EDT found the pressure had dropped 2mb, to 1000 mb. Top reliable surface winds seen by the Air Force plane with its SFMR instrument as of 9:45am EDT were 41 mph, at 8:10 am EDT. 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 10 - 15 knots of wind shear. The shear is from strong upper level winds out of the north. Since the atmosphere to the north of Don is relatively moist, the moderate shear will not be as damaging to the storm as if these winds had been blowing from the northwest, where the driest air lies. Thus the shear direction is often just as important as the strength of the shear, and in Don's case, the shear direction should not force significant amounts of storm-disrupting dry air into the core. Water temperatures in the Gulf of Mexico are near 29°C, which is 2.5°C above the 26.5°C threshold typically needed to maintain a tropical storm.


Figure 1. Morning satellite image of Don.

Satellite imagery shows that Don is a very small storm. Thus, the storm is vulnerable to pockets of dry air and modest-sized jets of wind shear that we can't see from the relatively coarse-resolution data collected by surface stations, hurricane hunter flights, and satellites. The moderate wind shear over Don is keeping Don's circulation tilted so that the surface center is displaced from the center at higher levels. This tilt is keeping the storm from intensifying. Latest visible satellite loops show a modest increase in the intensity of the thunderstorm's near Don's center began at 9am EDT, but this could be a transient burst and not a sign the storm is undergoing intensification.


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 be a boon or bane for Texas? The state is currently suffering through its worst drought in recorded history, and 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. However, we have a Goldilocks problem. We can't have Don intensifying into a hurricane, or its winds and flooding might bring hundreds of millions in damage. Neither do we 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. This forecast is low-confidence, though, since Don's small size makes it prone to sudden changes in strength, either upward or downward. NHC is giving Don just a 14% chance of intensifying into a hurricane in its 5am advisory, but this could easily change upward if Don manages to overcome its vertical tilt and start consolidating an eyewall. I put the odds of Don reaching hurricane strength at 30%. None of the computer models is predicting Don will become a hurricane.

A small system like Don is relatively difficult to resolve in some of the computer models we use to forecast tropical storm track, and the forecast tracks of Don from these models have a higher spread than usual. For those of you wondering about your odds of experiencing tropical storm force winds, I recommend NHC's wind probability forecast, which is showing that Corpus Christi and Port O'Connor, Texas have the highest chance of 39+ mph winds: 40%.

I'll have a new post this afternoon.

Jeff Masters

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Jasonweatherman2011, im sticking to my guns and im gonna say that Don will become a hurricane just wait and see!
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I'm sure you'll correct me if I'm wrong, but I recall hearing that if the pacific was very active, it tended to show a less active atlantic season, and vice versa.

Is that the pacific as a whole, or just the eastern pacific?
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Quoting MississippiWx:


I miss DestinJeff.


not me....with his off-topic posts and 4th grade humor....he makes a mockery of weather-guessing!
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new blog...
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840. DFWjc
Quoting jasonweatherman2011:
who think don will be a hurricane!! i think its will be a tropical storm all the way!!


Before the last night tear down, i had it at min Cat 1..
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No reliable computer models show significant tropical development in the near future and I have to agree with the computer models here for a few reasons that I have noted here.

1) Developing TUTT over the Central Atlantic into the Eastern Caribbean: This will pretty much create a "wall" of hostile upper level winds and will inhibit tropical waves coming across the Atlantic from developing.

2) Deep subsidence across the Main Development Region: The combination of Saharan air coming across the entire Atlantic as well as downward motion and reduced instability in the region will limit convection.

3) Only isolated pockets of favorable conditions across the entire Atlantic Basin: The only area that is somewhat favorable for development at this time are the SW Atlantic as the rest of the basin deals with either deep layered dry air and high pressures or hostile upper levels or both.
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New Blog!
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Quoting scott39:
The conditions for Don WILL become more favorable. Its heading into LOW wind shear and a moisture enviroment. Don WILL be a cat 1 when he hits Rock Port Texas. You heard it hear first folks.
Now there is someone i agree with fully, Don is coming back baby!
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TS Don Floater - RGB Color Infrared Loop

Zoom,Boxes and TFP's availible
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Quoting AniStarr:
Just wondering and I'm just working off a blackberry but what does the 500 mb indicate what might happen


Mexico
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Q: Will we surpass 2010 in terms of total tropical cyclone numbers?

A. Yes
B. Maybe
C. Probably
D. Unlikely
E. No
Member Since: July 6, 2010 Posts: 113 Comments: 31537
Quoting Waltanater:
Thanks for the link. Will this update as time goes on or is this just the cone for this particular advisory? I need one that will update automatically. Does anyone know if this will do that or if there is another KML file I need? Thanks.


Only specific storm/advisory. Will not auto update.
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Just wondering and I'm just working off a blackberry but what does the 500 mb indicate what might happen
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Quoting NotCircumventing:
764,

Your county should have a Plan, with various areas assigned Levels or something to aid in when to evacuate.

These levels will corresponf roughly with storm strength, so emergency managers can respond without having to evacuate everyone when it is not needed, which makes matters worse.


Most Emergency Management Agencies in coastal areas plan for one cat. up from what is forcast. For example: Don is forcast to be a TS when it makes L/F, so EMA's are setting plans in motion for a cat. 1 storm. This gives room for growth of the system and allows EMS's to have enough resources in place to respond after the storm w/o having to evac too many people or worry too much about any pre-storm prep that should have been done. This also cuts down on any search and rescue that may be needed.

When it comes to hurricane/TS response, It's better to have too many resources available and have to send some home.
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Quoting jeffs713:


That is different than normal... how?


haha, yes i know 290 is usually a mess and it moves at a snails pace but that day it was completely stalled from 610 (furthest i saw it stalled to the east) all the way out to brenham where it picked up a little
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Quoting TomTaylor:
Cloud tops getting gnarly in the WPAC



Seems like the Western Pacific wants to make up for lost time. They are having one tropical cyclone after another.
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Marine Weather Discussion

Excerpt:


SAL AND FRESH TRADES DOMINATING THE TROPICAL N ATLC ATTM AHEAD OF NEXT LARGE TROPICAL WAVE. GLOBAL MODELS HAVE BACKED OFF OF DEVELOPMENT...IN GENERAL OF THIS TROPICAL WAVE CURRENTLY ACROSS THE CENTRAL ATLC. HOWEVER...STRONG NELY WINDS AND BUILDING SEAS 9 TO 10 FT AND POSSIBLY HIGHER WILL SPREAD INTO THE AREA SUNDAY WITH THIS WAVE. GFS IS FASTER BY 5 DEGREES OR SO WITH THIS WAVE...WITH UKMET JUST BEHIND...AND ECMWF SLOWEST.


Don't shoot the messenger

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Impressive Bowing Gust Front, west of the Slidell Radar

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823. j2008
Quoting MississippiWx:


Well, the anomalies were cooler for most of the "preseason" and throughout June. However, we have seen a change in July where the SSTs have had a significant spike overall. These SSTs that we are seeing now were not predicted and if they continue, it will mean serious business in the meat of the season.

You can attribute the warming of the temps to light trade winds and a neutral to negative NAO. We have also had very little in the way of large dust outbreaks this year.

That plus the bermuda high being stronger thn normal doesnt stack up well for anybody in the Atantic.
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Don is out of the shear, it shouldn't be a problem, or at least, not much of a problem, from here on out. The major problem it has to deal with is dry air. And with it being such a small system, it is very susceptible to entrain it.
Member Since: July 6, 2010 Posts: 113 Comments: 31537
Quoting NotCircumventing:
801,

Only after the Greek alphabet is exhausted do we proceed to using Pig Latin to discuss landfall locations.

I think that is 3002 now if you count all different variations.


I miss DestinJeff.
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Quoting nrtiwlnvragn:


Link
Thanks for the link. Will this update as time goes on or is this just the cone for this particular advisory? I need one that will update automatically. Does anyone know if this will do that or if there is another KML file I need? Thanks.
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The conditions for Don WILL become more favorable. Its heading into LOW wind shear and a moisture enviroment. Don WILL be a cat 1 when he hits Rock Port Texas. You heard it hear first folks.
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blog freeze up? im hitting F5 and no new posts....
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Quoting P451:
Steering on the other hand has changed. Seems more and more that regardless of intensity that the center texas coastline is the place Don will want to be.



Of note is how weak and open it is around the Texas coastline in the lower and mid levels.

I wonder if the track could end up slow and erratic towards the end there.



As some of us have been saying. ;)
Member Since: August 26, 2006 Posts: 16 Comments: 4766
To describe current weather conditions here in NOLA I would need a cow and a flat rock...

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Quoting usa777:


Not angry at all. Are you sure the ignore button is not in Matagorda bay?


Member Since: August 22, 2008 Posts: 12 Comments: 6010
Looks like a RGV track (The GFDL sure changed):
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Quoting MagicSpork:


Yeah, Allison was the weather equivalent of a kick to the groin...It came in swiftly, and just when you thought the pain would stop, it just kept going and going and going...fortunately, I was living in an upstairs apartment at the time


She was a nasty storm, the only time my area of the neighborhood had water ever reach past the sidewalk that is the only time me and my dad ever worried about flooding but so far it never has happened again. Or will Don do it? Dun Dun DUNNNNN!
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DON will be gone by sat/sun, but EMILY looms on the horizon and could be a big player next week.
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Cloud tops getting gnarly in the WPAC

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Quoting TropicalAnalystwx13:


I've still not figured out why this season is expected to be less active than last.

Do you know? From the answers I've heard, slightly cooler Sea Surface temperatures. But...that has been proven wrong, by you.



Well, the anomalies were cooler for most of the "preseason" and throughout June. However, we have seen a change in July where the SSTs have had a significant spike overall. These SSTs that we are seeing now were not predicted and if they continue, it will mean serious business in the meat of the season.

You can attribute the warming of the temps to light trade winds and a neutral to negative NAO. We have also had very little in the way of large dust outbreaks this year.
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807. BA
some hi-res sat. should allow you to see Don leaving harsh conditions and entering into more favorable conditions

http://srf.to/gomsat1
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Quoting GHOSTY1:


US 290 was stalled out


That is different than normal... how?
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Quoting MississippiWx:


The GOG cooled again on the last frame. I'm not liking how the SST anomalies are going up. I posted a comparison of the SSTs from 7/27/2010 and 7/27/2011 on the last page and the temps were actually warmer this year than last.
Yeah I saw that post, and you bring up a good point.

Here's a gif I made to make it easier to compare this year to last year

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Quoting angiest:


The storm Monday night? It *died* right before it got to my house.


That was the evening, your right, it was a little heavy but short, wish my video camera could have worked because it was a great light show
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just because the models show that wave recurving doesnt mean it will... once the wave gets closer to the islands we will find out
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting NotCircumventing:
714,

sorry if I may have angered you with my on-topic post of where Don will threaten with landfall.

Is it possible to Google Map directions to the Ignore button? Distance from here is about .33 inches.


I'm thinking...(atagorda-May ay-Bay)
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Quoting P451:
Afternoon everyone. Don continues his struggles and it does not appear likely he will shake them to any large degree.

1845Z imagery loops.


RGB:




RAINBOW:




The newest burst of convection close to the center but on the south side and likely to also be displaced south of the center. There is little to no chance the new burst will either wrap around or somehow stack itself over the surface circulation. Therefore the intensity of Don will remain at least constant - weak TS.

I wouldn't put much into the smaller isolated flareups far north east of the center. That has more to do with the unsettled weather to Don's NE than Don itself. What it does serve is a chance to observe the continued shear coming in from the N/NE. You can see them immediately torn apart and thrown southward.







thanks for taking the time to make those loops, I know they can be a bit of a pain
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Quoting jasonweatherman2011:
i never look at computer models that are more then 5 days out its a wait of time!! there are never right more then 5 days!!




Jason, just a few posts back you were saying that it was going to be a fish storm. I like some of the things you post but if you make a prediction stick with it!
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Quoting ProgressivePulse:
Reason I say that Patrap is that the convection occurring in the N semi doesn't have the shear streamers that the clouds to the east of them have. And why convection is now there to begin with.

think the shear is changing from north to east/southeast
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Quoting vortextrance:
The increase in forward speed has allowed Don to finally get out of the strongest sheer in the last 6 hours. Now the dry air is still an issue, but not a killer. We should see some steady strengthening. Link below to the shear tendency map shows Don getting slightly ahead of the shear.
Link


Agreed.
Member Since: July 6, 2010 Posts: 113 Comments: 31537
Looks like Don is finally starting to get its act together! The past hour or so has shown a rapid increase in towers building on the north side of the storm, with a big blowup on the sw side as well. Starting to affect the convection levels all along the coast from Houston/Galveston area over to Florida panhandle. I think Don is working along with the disturbance on the coast to create more convergence.
Whatever he does I DONT CARE- just so he dumps lots of water on TEXAS! He can just sit and dump water on us for a week for all I care....Looks like center is moving NW towards upper middle coast between Port Lavaca and Freeport??
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The increase in forward speed has allowed Don to finally get out of the strongest sheer in the last 6 hours. Now the dry air is still an issue, but not a killer. We should see some steady strengthening. Link below to the shear tendency map shows Don getting slightly ahead of the shear.
Link
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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.