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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Your area as well as others need the rain badly
What would make them do that? Are they seeing something strange?
Weird. Someone in that flight should take away the tequila from the pilot. XD
Your guess is as good as mine, maybe they are looping higher up or training for flying in an eye. It is crazy weird.
Not certain how this jives with the forecast path. Confusing. Is this a case of the left hand not talking to the right?
would rather see you mow your lawn than the prices of meat and crops go up so much that the rest of the USA cannot afford to buy groceries...if you dont want to mow...dig up your grass and pave your yard with green concrete...
This is the 27th straight day over 100, but I could feel something different in the air today from the beginning. The clouds were looking rather ominous and, it was nearly 1:00 before the signs around town started registering triple digits. I was thinking maybe today's high would be only like 102 instead of a more typical for this heat wave 107.
As I walked out of the theater this afternoon the humidity hit me in the face and I spotted what looked suspiciously like the aftermath of a brief shower on the pavement. The little spots of quickly evaporating wetness were no match for the high pressure ridge of doom though, and were fading fast. I put my headphones on and headed towards my bike when it started raining again, and I took shelter under an awning. As the humidity went from ridiculous to hard-to-breath I stood watching this piece of pavement in front of me get rained on for 18 minutes (2.5 plays of Radiohead's Street Spirit heh) without it getting wet. It was as if the pavement didn't quite remember what to do when it got rained on. 30 minutes later though, the sky opened up and we got our first measurable rain of July and the temperature is now in the 80's. Quite nice!
Good for you, happy that you received some rain
they showed a nice brand new one last year on the news...did a whole segment when they were tracking a storm...got one the year before that too...
They are being controlled by aliens! LOL
Wow, now Im really confused. What are they doing?
hes on HCW now.
Wondering how much fuel are they wasting on those loops O_O
No tiger, just looked it up. The plane in question known as "Kermit" was built in 1975.
URNT12 KWBC 282225
VORTEX DATA MESSAGE
A. 28/2153Z
B. 24 DEG 13 MIN N
91 DEG 26 MIN W
C. NA
D. NA
E. NA
F. 136 DEG 36 KT
G. 046 DEG 80 NM
H. EXTRAP 1004 MB
I. 16 C/2566 M
J. 17 C/2549 M
K. 17 C/NA
L. NA
M. NA
N. 1345 / NA
O. 1/2 NM
P. NOAA2 0304A DON OB 07 AL042011
MAX FL WINDS 36KT NE QUAD 2130Z
SLP EXTRAP FROM 750MB
Flight 3, NOAA HH
Don is doing the opposite it did yesterday, looks like it hit a sweet spot. With convection growing and stronger while we get closer to D-min Don should strengthen tonight.
And that has been said thousands of times but ehh... mind you I wanted to say something. xD
Why would they show a public Vortex message if the equipment was foul though?
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