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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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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Quoting GHOSTY1:


your asking for the 2001 TS Allison scenario that one was a doozie for us in Houston


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
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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.







I gotta disagree the mets are saying that conditions are gonna become more favorable which they maybe already starting to do so i believe Don may be beginning to drag in some moisture for some extra convection
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Don will strengthen right before landfall.
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Quoting Waltanater:
Anyone know where I can download the KMZ or KML file for live feed to install in Google Earth? I need one that includes the cone of uncertainty. Thanks.


Link
Member Since: September 23, 2005 Posts: 14 Comments: 11211
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.


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.

Member Since: July 6, 2010 Posts: 113 Comments: 32257
1010mb low with catl wave 7N 36W moving west or north of west. the system should be in the vicinity of the windward/leeward islands mon afternoon. what is frightening, most of the models develop this system into a cyclone
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Quoting TropicalAnalystwx13:
Don firing deep convection once again, and according to ATCF, no change in pressure since 12Z (1001 mb.). Could this be the start of Don's intensification? Possibly, but it is a little too early to see yet. Multiple outflow boundaries are seen coming from the system, which means that the main problem that Don is having is dry air.


Yeah, that's what I see too. There's a lot of air falling out the bottom of this thing. Never a positive indicator for intensification, and if you watch the precip. runs towards the end, you can actually see the system sucking in that dry air. Watch the light green disappear, as if it was literally being eaten by Don. There's not much left though. It may wall itself off by this evening.

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Quoting hydrus:
Plenty of fuel for tropical waves...Get rid of the dry air, add some upward phase, and the above average forecast numbers will come to fruition...



I think the dry air is an attribute we'll have to deal with this year in the E-Atl and not to uncharacteristic of a Neutral ENSO year. MJO is coming around the mountain so to speak, should be here in the next week or two.
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Quoting GHOSTY1:


True that because i live in the NW houston area, Jersey Village, and the only rain we got was a few nights ago and it was mostly a awesome light show but did little good before that it has been monthes since we got a good amount of rain


The storm Monday night? It *died* right before it got to my house.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
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!!


The models develop it in that time frame (around 144 hours).

Quoting ProgressivePulse:



I think he's talking about the re-curvature point which is too far out.


Oh.
Member Since: July 6, 2010 Posts: 113 Comments: 32257
Invest 91L "Coming Soon"
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The models will move with these large fluctuations in strength. The TCVN is still relatively close to the current NHC track, I don't think they will move it much unless that moves as well.


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Quoting ProgressivePulse:


Waves are sure getting tall, going to get busy soon.
Plenty of fuel for tropical waves...Get rid of the dry air, add some upward phase, and the above average forecast numbers will come to fruition...
Member Since: September 27, 2007 Posts: 1 Comments: 21414
It looks like Don is pulling in moisture from the north and getting more organized. What is the reason for the forecast of it to curve more westerly? Looks like it's maintaining it's Northwest course pretty well. Don seems to be doing much better than last night though.

Sorry, another question- Does Dmax and Dmin affect sorm rainfall during land, or does it just correspond with cloud height?
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Anyone know where I can download the KMZ or KML file for live feed to install in Google Earth? I need one that includes the cone of uncertainty. Thanks.
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Quoting smartinwx:
question...along the gulf coast, what strength storm will prompt an evacuation? Does it depend on the area? Like some areas a TS would force one, whereas others a Cat 1 would?


It's a city discretion thing, i live in NW houston so i dont usually worry about EVAC but when we need information our city (Jersey Village) has boxes on the stop signs at major intersections around the neighborhood that detail the situation and when and what to do for the worst. Hope that helped and someone who lives around galveston or corpus could probably answer better.
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Southeast Texas does not need Don they have Easterly wave affecting them today and Friday giving them more rain than Don will give Texas most likely. AVIATION...AN INVERTED UPPER LEVEL TROF OR EASTERLY WAVE HAS
MOVED INTO EAST TEXAS AND THE WESTERN GULF. THE TERMINALS ARE ON
THE EASTERN OR WET SIDE OF THIS TROF WHICH HAS RESULTED IN
INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS
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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 2 inches.


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


Fair point.
Member Since: September 3, 2007 Posts: 0 Comments: 527
772. JRRP



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Quoting HurricaneHunterJoe:
if Don gets organized better , he may go further south and likewise if he weakens,he go further north, i thought corpus was a good landfall site, where does corpus lie in your lines?


I can't see Don strengthening much anymore, so Corpus Christi will probably get what's the "worst" part of Don.
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Quoting TomTaylor:
SST Anomalies over the last 3 weeks



Seems like the entire Atlantic has heated anomalously. By the end of the loop, the Gulf, Caribbean, MDR, and Gulf of Guinea all appear to have warmed some. All of which will favor increased activity, except for the Gulf of Guinea warming. Although the Gulf of Guinea is still anomalously cold.


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.
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Quoting TropicalAnalystwx13:


The models develop it less than a week away. Not too far out.



I think he's talking about the re-curvature point which is too far out.
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766. JRRP
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Quoting MississippiWx:
Wow, the Atlantic has become very warm in the past week. It is now warmer than this time last year.

July 27, 2010:



July 27, 2011:

nice point, that is very interesting to note that the Gulf of Mexico, Caribbean, Main Development Region, and Mid Atlantic are all warmer than they were at this time last year. Cape Verde region is maybe a little cooler, but still.

Here's a gif to compare the two years for the 27th of July

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question...along the gulf coast, what strength storm will prompt an evacuation? Does it depend on the area? Like some areas a TS would force one, whereas others a Cat 1 would?
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Quoting TropicalAnalystwx13:
Sorry to deviate off Don, but the ECMWF is once again showing a tropical cyclone affecting Puerto Rico and Bahamas, but recurves it out to sea (good thing, because if not, it could get real strong. Could do that anyway).

Yes, it should be a TC, since its closed.


not good news i need some rain here on the south east coast :) ill take a cat1
Member Since: July 25, 2011 Posts: 0 Comments: 1102
Quoting jasonweatherman2011:
Sorry to deviate off Don, but the ECMWF is once again showing a tropical cyclone affecting Puerto Rico and Bahamas, but recurves it out to sea (good thing, because if not, it could get real strong. Could do that anyway).

to far out from now!!


The models develop it less than a week away. Not too far out.
Member Since: July 6, 2010 Posts: 113 Comments: 32257
Blog update! Read for my full opinion.
No change to Don, new African wave worth watching 7/28/11
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Weather channel says close to coast where Don makes landfall 3 to 4 inches is possible, other areas will average around half an inch or so but overall this is not a rainmaker for Texas unfortunately unless he comes over your house basically.
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Quoting angiest:


On the east side. Those of us out west of Houston are still bone dry.


True that because i live in the NW houston area, Jersey Village, and the only rain we got was a few nights ago and it was mostly a awesome light show but did little good before that it has been monthes since we got a good amount of rain
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Could be a pretty impressive storm tomorrow morning, comparatively speaking.
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Quoting floridaboy14:

you are certainly correct. dry air will be its problem until landfall shear however will become MUCH weaker for it tomorrow. has the potential to be a moderate/ strong ts 50-65mph not a hurricane but still a nice ts


I don't think dry air will be as much of a problem as you think. There is a lot of moisture in the Northern and Northeastern Gulf that is moving West and will meat up with Don as it approaches Texas. We've had 3 days of rain here in the FL Panhandle and all that moisture is now moving West around the High. I sure hope Don pulls it all in and sends it to Texas, they really need the rain.
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Looks like all the models have finally converged on a South Texas landfall. The only question is whether Don has enough punch to make its way far enough inland to dump any significant rain on Central Texas. Austin has scattered showers forecast for Saturday.
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754. HCW
Quoting DFWjc:


Is it really worth the money??


It's great when you are driving over 60mph cause you don't need wipers at all but at lower speeds it's not very impressive. I use it all the time while chasing cause wipers mess up the quality of my live stream. If you have any other questions feel free to shoot me an email. Now back to Tropical Storm Don
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Quoting hydrus:
72 hours..


Waves are sure getting tall, going to get busy soon.
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Quoting thirdcoastguy:


We all need the rain. It is worse here than Houston area. Ya'll have got a little rain lately.


On the east side. Those of us out west of Houston are still bone dry.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting cctxshirl:

I hope so. Rockport works for me-lots of our wildlife are dying. Fire Dept. came and hosed down the "Big" Tree at Goose Island to save it from death.


When did they do that? It didn't look too bad off last month.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
USA700, chill out he just making his opinion and like he said there's a ignore button, but as far as i know he has made some pretty good ideas and opinions. Not trying to be rude just my take on the situation.
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Don does not look like a big rain maker at this time..
Member Since: September 27, 2007 Posts: 1 Comments: 21414
Quoting GHOSTY1:


You may be in the good area because most meteorologist predict rockport landfall and victoria isnt too far away so you may get some good rainfall totals i just hope we can get some here in houston too, Good luck!


We all need the rain. It is worse here than Houston area. Ya'll have got a little rain lately.
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SST Anomalies over the last 3 weeks



Seems like the entire Atlantic has heated anomalously. By the end of the loop, the Gulf, Caribbean, MDR, and Gulf of Guinea all appear to have warmed some. All of which will favor increased activity, except for the Gulf of Guinea warming. Although the Gulf of Guinea is still anomalously cold.
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Someone shoot some fertilizer into Don and help him grow. Weather Channel showed quarter of an inch rain projections for South Central Texas, now that is disappointing.
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Quoting GHOSTY1:


Thats news to me, thanks for letting me know, doesnt that sound like they are thinking it may be stronger than a tropical storm or are they just being precautious?


It is a percaution. Here is the TAMUCC release to staff http://www.tamucc.edu/marcom/hurricane/assets/wea ther_update_7-28.pdf
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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.