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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El Nino, or La Nina conditions?
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Quoting jasonweatherman2011:
east coast is save from any hurricane or tropical storm for the next two weeks or more!!

not guranteed.. there should be a trough next week but how strong it is and if a storm forms will depend on timing
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642. HadesGodWyvern (Mod)
Philippines Atmospheric Geophysical Astronomical Services and Administration
Tropical Cyclone Bulletin #2
TROPICAL STORM KABAYAN (MUIFA)
11:00 PM PhST July 28 2011
==============================

Tropical Storm "KABAYAN" has intensified further as it moves west northwestward.

At 10:00 PM PhST, Tropical Storm Kabayan (Muifa) located at 12.4°N 133.6°E or 890 km east of Catarman, Northern Samar has 10 minute sustained winds of 40 knots with gusts of 55 knots. The cyclone is reported as moving west northwest at 9 knots.

Additional Information
=========================

This weather disturbance is too far to directly affect any part of the country.

The public and the disaster coordinating councils concerned are advised to take appropriate actions and watch for the next bulletin to be issued at 11 AM tomorrow.
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Mr. Masters give Don a 30% chance of becoming a hurricane i agree within that range but i give a 40% chance
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Quoting TropicalAnalystwx13:
0Z ECMWF @ 168 hours - Tropical cyclone affecting Puerto Rico:



0z ECMWF @ 192 hours - Weakening due to interation with Hispaniola.



0z ECMWF @ 216 hours - Affecting the Bahamas as a strong system.



0z ECMWF @ 240 hours - Trough split off GA/SC coast, system affecting Bahamas now curving out to sea (I think?).

Well it shows a strong vorticity max associated with the tropical wave...not a tropical cyclone.

It could become a tropical cyclone, however, so we'll have to watch it. Right now dry air ahead of it, the broad disorganized nature, and only marginal upper level winds should prevent it from developing over the next few days. Like you said, though, we'll have to watch it after it passes the east Caribbean. Slight development just before entering the Caribbean is also possible, as the CMC is showing.
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The cloudiness north of Don is consistently increasing, and may soon re-envelope the north side of the circulation. Additionally, that large burst of convection near the COC show Don has some staying power. Methinks he's not done yet.
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Vort is decent with that wave too.
Member Since: July 8, 2005 Posts: 259 Comments: 24574
Waiting for the next image of Floater One. Looks like Don is the little engine that could, he's just a chugging along, best he can.
Member Since: June 11, 2008 Posts: 0 Comments: 47
12z ECMWF is picking up on a low pressure area traversing across the Atlantic with a good amount of vort, equal that of Don.
Link

And here's that wave, this could be mentioned as soon as 2 am.
Member Since: July 8, 2005 Posts: 259 Comments: 24574
Quoting oreodogsghost:
Nice dark clouds forming up over Houston now.


Yea i noticed too but sadly not getting any rain in our area well at least some are getting some rain showers.
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Quoting NotCircumventing:
Don, you coulda been somebody. You coulda been a contender!


LOL
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Member Since: September 27, 2007 Posts: 1 Comments: 22601
Nice dark clouds forming up over Houston now.
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Quoting NotCircumventing:
Don, you coulda been somebody. You coulda been a contender!


Nice
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Quoting HurricaneHunterJoe:
he might start refiring and get more organization if he gets out of that northerly shear
maybe the easterly/southeasterly shear he will be going into will be alot better for him, cuz the northerly is killing him
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Despite my pessimistic attitude towards Don, it certainly could still ramp up by the coast like Humberto did. Right now is kind of saddening though, because as the convection wanes so does the chance of rain in TX.
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Quoting hydrus:
Naturally the CMC has it cranked up to hurricane strength ..



Getting to be that time of year however, Biggies around the corner no doubt.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
When the meteorologist say there may be a chance for a minimal cat. 1 hurricane they're probably certain theres a pretty good chance of it but dont want people to get all stirred up
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12Z HWRF shows weak system..
Also, 12Z shows nothing on potential Emily...

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Turning toward the WPAC...

Tropical Storm Nock-Ten which had been hanging around and intensifying just west of the Philippines causing torrential flooding and killing several people, is now over the South China Sea. Slight intensification should occur over the next 24 hrs as vertical wind shear is light, moisture is plentiful, SSTs are warm, and upper level winds are fairly anticyclonic providing divergence aloft. Within the next day, Nock-Ten should make landfall on the island of Hanoi. Afterwards, it will temporarily reemerge over water in the Gulf of Tonkin, before making landfall again, this time in Vietnam.




Meanwhile, another tropical storm has formed in the Philippine sea, tropical storm Muifa. Fortunately for the Philippines, this storm should not affect the island nation as it is pulled to the north, first by a trough to the NE of Japan, and then by a high currently over the central pacific which will be building in over the WPAC. Looking at upper level conditions, right now wind shear is not the best as it is currently between 15-25 knots over the system. Light anticyclonic flow is providing divergence aloft over most of the system, however, north easterly winds on the east side of the system are pushing air towards the system on the NE side, providing convergence aloft. Despite this, convection has managed to become very intense over the system (< -90C) thanks to the very warm SSTs over in the WPAC as well as a very moist environment. These factors will continue to allow Muifa to gradually strengthen, despite only decent upper level conditions. The big question right now is the track, and whether or not this will be another landfall for Japan. Right now there is quite a bit of disagreement among the models and this is reflected by the large cone of uncertainty in the JTWC forecast.




So, we'll have to watch as time progresses and this storm gets more developed as the models will be able to get a better sense of the track by that time. Main things to take away from this is gradual intensification should occur as it tracks slowly northward. Shouldn't be much of a concern for the Philippines, but Japan, China, Taiwan, and Korea will all have to keep an eye on this one as it looks like it should continue northward, turning more northwestward by next week as blocking over western Russia, China, and Mongolia should prevent any troughs from pulling it out to the east and ridging builds in from the east.

ECMWF and GFS 500mb 8-10 Average Anomalies Comparison

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Quoting prcane4you:
don is nothing,poor bloggers.


They're interesting when they go up or down. Observing them is how we learn. :-)
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Guys look at the recent blowup of convection. don is struggling yes but it wont dissipate until making landfall
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12Z HWRF shows weak system south of Corpus

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Quoting jasonweatherman2011:
something is spining here
so.
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he might start refiring and get more organization if he gets out of that northerly shear
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Once again everyone is back to RIP Don mode, if TWC and the NHC think that it will strengthen slightly then i'm pretty sure he'll live and probably be a little stronger than predicted.
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Quoting ncstorm:
Day 7 of the North American Hemisphere..if I am reading this map right, it looks like the bermuda high isnt that strong..leaving the east coast door wide open..


Secondary weather: And the Pacific high is bringing warm weather over here in California! or is it the other high in NV

Now back to Don
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Quoting ProgressivePulse:


MJO is coming around the mountain too...
Naturally the CMC has it cranked up to hurricane strength ..
Member Since: September 27, 2007 Posts: 1 Comments: 22601
don is nothing,poor bloggers.
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Latest steering continues to support more NW motion for the time being.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
What will happen with the moist air coming in from the north, will it help to strengthen the system?

Really curious about this, had posted it a bit back. TIA response.
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Don vs. Dolly = no comparison

Dolly


Don

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Now that don is having some prohlems does that have any effect on the track?
Member Since: August 19, 2007 Posts: 0 Comments: 342
Quick! Everybody in Texas turn on their sprinklers!
And leave them on to moisten the dry air that's sucking the life outta Don.
sigh... If only drought-busting were that easy.
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T.S.Don is unorganized..
Member Since: September 27, 2007 Posts: 1 Comments: 22601
Quoting floridaboy14:
when don makes landfall how strong will it be?
a: td
b: nothing at all
c: ts 40-50mph
d: stronger than 50mph im going with c



D here. I think this recent weakening will reverse course in due time and Don will get back on schedule.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
or is my thought process incorrect?
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Quoting TropicalAnalystwx13:
There is good model support for Tropical Storm Emily next week. Looks like we will not be as quiet as originally thought.


MJO is coming around the mountain too...
Member Since: August 19, 2005 Posts: 5 Comments: 5458


looking at this, it appears that Don will be leaving that 20-30 northerly shear and get into an area more hospitable for strengthening? shear will go from north to easterly or southeasterly and weaken some?
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I think Don is going to come ashore as a DUST DEVIL.
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when don makes landfall how strong will it be?
a: td
b: nothing at all
c: ts 40-50mph
d: stronger than 50mph im going with c
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I'm not sure Don will even bring much rain anymore, very sad.
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the circulation is still strong and partially exposed. sure dry air is killing it but i dont think it will kill it to northing
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Quoting angiest:


Are you sure that's all outflow? At least some of it looks to be pulling inward, like it is attempting to build some feeders (not necessarily succeeding.)
Yeah, some inflow is apparent, but there are a lot of outflow boundaries.
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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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