Don battling dry air and wind shear
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
Reader Comments
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LOL!! I'm the same way with swirling water down the drain! My mind instantly says "tornado"
They can declare an invest at any percentage, it is up to the forecaster. Remember the other day when Don was at near 0%, they reactivated him. Even before that, I think he was first declared at 10%.
We will see 91L tomorrow, hopefully.
Yes?
No...Don is at 998 mb.
Or TexMex
Lol...That's funny, but messed up.
Eh, it's kind of a mixed bag. I've been through 100 mph winds, yet I have refused to evacuate in the event of another one (unless it's exceptionally severe). My family says they are, but I will stay behind and capture the footage on film.
Then again, I am 70 miles inland, so the storms I do get typically weaken quite markedly by the time they make it this way.
Not what the latest vortex says...
They are both right, but I think 20% more than 12 hours it becomes an invest!
Yep , you're right, I was just speaking generally!
The ECMWF isn't actually developing the CATL wave. When I looked earlier, it was only indicating one closed isobar, which isn't at all equivalent to a full-fledged tropical cyclone.
Im sorry i said it incorrectly i didn't mean in windspeed and strength i mean i would want a large system that would be able to aleviate our drought, sorry for the misunderstanding. I live in Houston and remember Ike i was without power for 3 weeks and was lucky all the trees didn't fall on my house or the neighbors. I know many were horribly ruined by the hurricane such as Bolivar Peninsula, Galveston, etc. i know the consequences that Ike brought and i wouldn't welcome anything like that here. Sorry for miscommunication.
The latest vortex wasn't dropped in the eye.
I agree about the moisture part. But it is bad form to cite a storm which left tens-to-hundreds of thousands without power for anywhere from 1-3 weeks and access to Galveston Island cut off for over a week afterwards. Many lost their homes and have yet to recover.
I get your point. However, the cotton farmers are just a few weeks away from harvesting. Too much of a good thing (ie - rain) would be detrimental for them. Let's hold off a couple more weeks before we pray we get too much.... I'm a rancher, born and bred, but I can buy hay (albeit at a higher price right now)- the grass is already dead as is everything else we've planted. Let's pray the cotton growers get theirs in before the Lord gives us a break.
1.) It is still embedded within the ITCZ. No designation until it separates.
2.) It lacks a lot of organized deep convection. Until then, probably not a designation.
3.) It probably lacks the wind speeds needed, so no designation until then.
It may be able to fix all these by Monday, but it will be a close call. Until it does, we won't have a TD/TS out of this.
The key word that the original post says is "hints".
You can see why people would be sensitive. Imagine if Ike was a Cat 3 4 or 5
Cheak in the morning and see how strong Don is, then make your decisions. One thing I've learned is that these storms can change quick.
LMAO!!!!
No problem. It's hard to read people's intent sometimes on the internet. :)
So you gonna get mad at me for asking for multiple storms to hit Texas and you make dirty jokes up? Your maturity value is minimal. Think before you speak.
didnt you just apologize? Didnt i just accept?
Btw an immature joke is not the equivalent of what you saidl
LOL. That just doesn't make any sense, on a couple of different levels.
Ha! Was waiting for that.
Best case scenario (in terms of recurvature probabilities) would be for pre 91L to strengthen significantly, as it would increase the likelihood of it feeling a profound weakness within the subtropical ridge.
Don't see that happening, though; rapid development, I mean -- though recurvature may still be a possibility depending on the evolution of the synoptic scale pattern.
Ah, yes. My bad. :P
I couldn't help it :P, sorry if I offended though.
Designation of an invest does not need any of these things
How amusing. Sad, but amusing.
I live about the same distance inland. My evacuation requirements are a Cat 3 or higher hitting between roughly Bay City and the Bolivar Peninsula.
The builders made a mistake when they put my roof on, and I don't want to be here to find out if the fix worked correctly (the purlin struts were installed at too shallow an angle. A second set was installed), and not living on the coast, no hurricane straps. Plus, kids don't like storms, and the little one (who has cystic fibrosis) doesn't need to be without power and A/C. So, it makes sense to give them a trip to the grandparents.
I should reword that. I was talking about for TD/TS designation.
Was this official there for Alex's rains last year? Houston got a fair amount of flooding from him.
Your right i may have gotten a little to aggresive with our need for help i hope for the best for everyone. I had a question though, My family and i go to Rockport alot and we drive by cotton fields on the way there but they seem to be down in numbers to, is it just the farms we go by? I hope you have good luck in your future and you have a good harvest.
Screw the models, they've performed horrible this season.
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