Don battling dry air and wind shear

By: Dr. Jeff Masters , 7:37 PM GMT on July 28, 2011

Share this Blog
24
+

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

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 321 - 271

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52Blog Index

Don has looked worse than he does now. There is actually some expansion of the convection towards the north and outflow has improved substantially. It's only limited on the northeast side of Don at this time:

Member Since: Posts: Comments:
320. DFWjc
Quoting Tazmanian:



i would watch what you post on here guys there are times that you can post photos that dos not have too do with the weather then there times that you cant



During active periods of hurricane season, these rules will be strictly enforced. Violations will be met with a minimum 24 hour ban.


And who gives out these "ban hammers"? just wondering...i didn't see it in the "rules"...
Member Since: Posts: Comments:
NORTH, Don. NORTH. Mexico does not need you.
Member Since: Posts: Comments:
Quoting DFWjc:


does it look like sudden moment to the West?


It sort of looks like it but we gotta watch for maybe the next few hours to see for sure
Member Since: Posts: Comments:
Quoting nigel20:
Is don now strenghtening?


actually all of the opinions on here have Don as this: Don is under shear anywhere from 5 to 40 mph...it is strengthening while it is weakening, growing while it is shrinking, becoming better organized while it is dying, taking a northward jog as it goes south, stacking while it is collapsing...i think i got it all...

not trying to be sarcastic but for people that are new and do NOT understand the physical make up of a storm, all of this can be really confusing... i know enough to be able to read the charts, maps and know why the models see what they do and that there is error in the models...but to those of you who are screaming about what is going on...post a chart or map to prove what you are saying so the newbies can learn...
Member Since: Posts: Comments:
Quoting miguel617:
Time to stock up on some tequila!
img src="">



i would watch what you post on here guys there are times that you can post photos that dos not have too do with the weather then there times that you cant



During active periods of hurricane season, these rules will be strictly enforced. Violations will be met with a minimum 24 hour ban.
Member Since: Posts: Comments:
Quoting cloudburst2011:



please read and understand what i said...I DID NOT SAY HE WOULD FALL APART...I SAID THE SHEAR WOULD KEEP HIM IN CHECK ANOTHER WORDS TO PUT IT SIMPLE FOR YOU NOT STRENGTHEN...


Don't get so excited and i don't know if you meant to be yelling because thats what all caps usually mean or if you were just trying to make a point. There was no inflammatory statement meant that was why i added the smiley face i was just speaking my opinion.
Member Since: Posts: Comments:
312. DFWjc
Quoting GHOSTY1:


It appears so but others don't want to believe it


does it look like sudden moment to the West?
Member Since: Posts: Comments:
Quoting tiggeriffic:
wow...from what i am reading Don is under shear anywhere from 5 to 40 mph...it is strengthening while it is weakening, growing while it is shrinking, becoming better organized while it is dying, taking a northward jog as it goes south, stacking while it is collapsing...i think i got it all...


+1 LOL
Member Since: Posts: Comments:
Quoting nigel20:
Is don now strenghtening?
Ask that question in a couple of minutes the HH are almost there they have reached already to 35mph winds and are closing in on the center
Member Since: Posts: Comments:
Quoting nigel20:
Is don now strenghtening?


It appears so but others don't want to believe it
Member Since: Posts: Comments:
Time: 21:33:30Z
Coordinates: 25.1333N 90.2833W
Acft. Static Air Press: 750.5 mb (~ 22.16 inHg)
Acft. Geopotential Hgt: 2,580 meters (~ 8,465 feet)
Extrap. Sfc. Press: 1008.9 mb (~ 29.79 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 132° at 35 knots (From the SE at ~ 40.2 mph)
Air Temp: 14.6°C (~ 58.3°F)
Dew Pt: 11.2°C (~ 52.2°F)
Peak (10s) Flt. Lvl. Wind: 36 knots (~ 41.4 mph)
SFMR Peak (10s) Sfc. Wind: 31 knots (~ 35.6 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data
Member Since: Posts: Comments:
Quoting CorneliaMarie:
Man this time yesterday it was in overload.



You mean "overdrive".

A blog can not be in overload. It can be overloaded though.


Okay then it it was traveling at a blistering pace with a blatant disregard for the law.
Member Since: Posts: Comments:
Is don now strenghtening?
Member Since: November 6, 2010 Posts: 11 Comments: 7819
From TWC:

A well-defined tropical wave is over the tropical eastern Atlantic, almost half way between Africa and the Windward Islands. The wave has a broad area of rotation with numerous areas of showers and thunderstorms. Some models suggest the potential for eventual development of this system, since upper-level winds are forecast to be weakening as the system moves over increasingly warm waters in the central Atlantic. The system should reach the Windward and Leeward Islands on about Monday of next week.

Maybe TWO mention at 8 EDT
Member Since: Posts: Comments:
Quoting tiggeriffic:
wow...from what i am reading Don is under shear anywhere from 5 to 40 mph...it is strengthening while it is weakening, growing while it is shrinking, becoming better organized while it is dying, taking a northward jog as it goes south, stacking while it is collapsing...i think i got it all...


well duh isnt it obvious? :p
Member Since: Posts: Comments:
wow...from what i am reading Don is under shear anywhere from 5 to 40 mph...it is strengthening while it is weakening, growing while it is shrinking, becoming better organized while it is dying, taking a northward jog as it goes south, stacking while it is collapsing...i think i got it all...
Member Since: Posts: Comments:
Quoting cloudburst2011:


dont hold your breath you are fighting a losing battle just sit back and watch...they will see ...


We'll just see Cloudburst, Don is done yet, yalls opinion that he will be sheared apart is fine its your opinion but the death of Don has been goin on for days and he never dies so is that the more times you say he'll die the chances increase. Just remember if you lose the battle that doesn't mean you'll lose the war (i didn't state the phrase correctly because the war isn't over with yet :)
Member Since: Posts: Comments:
Quoting HimacaneBrees:
Did the blog go poof? Man this time yesterday it was in overload.

Because Don was about to form.
Member Since: Posts: Comments:
I am a regular here (and discuss blobs, speculate, look at model runs, etc. all day) but once a storm actually forms, I tend to sit back and watch the NHC output and forecasting for the outcome. They have some of the best tropical forecasters and computers and models, at their disposal (the ONLY Official Source)in the world and they have to try to get it right at main place where it really counts; intensity and general location of landfall. They are always working on improving intensity forecasting but their general track and warning/watch system works very well (the 3-Day track) adjusting accordingly as conditions merit closer to landfall. My point is I don't second guess their forecasting unless there appears to be a glaring error somewhere and rapid intensification (or not in the current case with Don) in one of the most unpredictable elements out there. NHC has all of my respect and I don't think much of the bloggers who second guess NHC all the time without any credentials to back it up.
Member Since: Posts: Comments:
Quoting Max1023:
Just north of Don the shear is higher, Don is on a shear gradient where the center itself is experiencing about 15 knots. Those storms north of Don are under 30-40 knots of shear.

yep.

it's quite easy to see that NE of Don the winds are quite strong and shearing it badly.
Member Since: Posts: Comments:
Did somebody mentioned that the CATL wave will have a yellow circle by tomorrow?
Member Since: Posts: Comments:
TS Don is the most organized it has been all day. That isn't saying much as its still not very impressive, but could be moving upwards to 45kt intensity, according to ADT.
Member Since: Posts: Comments:
Did the blog go poof? Man this time yesterday it was in overload.
Member Since: Posts: Comments:
people the system is small.. small system are much more affected by shear and dry air then large ones.. there is NOT more than 15 knots of shear over Don. its going to get better and most likely will make landfall south of courpis christi with 50 to 65mph winds
Member Since: July 25, 2011 Posts: 0 Comments: 1102
04L/TD/D
on approach


Member Since: Posts: Comments:
Quoting P451:


The center is on the northern edge of a convection plume that is stretched hundreds of miles southward.

This is beyond the idea that a small system is more susceptible.

The values are wrong.

The proof is right there in all the imagery.


Relax it seems things are gettin a little tense, its just his opinion, my opinion is that even with the cloud tops blown hundreds of miles south that doesn't mean that the storms are dying, they could be continually firing under it and the shear is to no effect, jmo.
Member Since: Posts: Comments:
Quoting P451:


The center is on the northern edge of a convection plume that is stretched hundreds of miles southward.

This is beyond the idea that a small system is more susceptible.

The values are wrong.

The proof is right there in all the imagery.


The main convective mass itself isn't very elongated. Wind shear that you're describing would make this small of a cyclone signficantly more deteriorated. The center WOULD be exposed.
Member Since: Posts: Comments:
Quoting P451:


Does 15kt of shear displace convection 100s of miles though? I don't think so - small storm or not. I think the shear values are incorrect.

Look at the storms far to the north east as well - they have been torn apart leaving trails several hundred miles long in just a few short hours.

That is some pretty intense shear.

The values on the maps must be understated/incorrect.

I will take what I can see on satellite imagery over maps that have been wrong before.

We're expecting CIMSS to be correct. We know what we see on satellite imagery. The two do _not_ correspond with each other. Given the satellite is real time imagery - and the shear maps are computer generated overlays - I think there is no reason to trust the CIMSS maps right now.


P451, I think the reason they look like it is more is because the thunderstorms to the north of Don are moving Northward at about 10 mph. Creating a net shear of 25knots, which is what you are stating.
Member Since: Posts: Comments:
281. HCW
Pinhole Eye j/k


Member Since: Posts: Comments:
Just north of Don the shear is higher, Don is on a shear gradient where the center itself is experiencing about 15 knots. Those storms north of Don are under 30-40 knots of shear.
Member Since: Posts: Comments:
Quoting Tazmanian:



lol it looks like DON wants too go too MX
taz it may landfall 3 miles south of the texas border with mexico i think maybe close to 26 n no further
Member Since: Posts: Comments:
Quoting PrivateIdaho:


CRY DON CRY!!



LoL, gotta love Ermey, but i have a feeling even Ermey likes Don thats probably whats keeping don going, Ermy is forcing him to go all the way.
Member Since: Posts: Comments:
Quoting JrWeathermanFL:

Does that men that he will be ripped apart soon?


No, it doesn't, because shear is not that high. It's 5-15 knots, no higher.
Member Since: Posts: Comments:
Quoting P451:


Does 15kt of shear displace convection 100s of miles though? I don't think so - small storm or not. I think the shear values are incorrect.

Look at the storms far to the north east as well - they have been torn apart leaving trails several hundred miles long in just a few short hours.

That is some pretty intense shear.

The values on the maps must be understated/incorrect.

I will take what I can see on satellite imagery over maps that have been wrong before.

We're expecting CIMSS to be correct. We know what we see on satellite imagery. The two do _not_ correspond with each other. Given the satellite is real time imagery - and the shear maps are computer generated overlays - I think there is no reason to trust the CIMSS maps right now.


Not to be rude or anything, but it isn't the map that is wrong. It's your analysis. If shear was really that high, this system wouldn't be organizing right now.
Member Since: Posts: Comments:
Quoting P451:


Does 15kt of shear displace convection 100s of miles though? I don't think so - small storm or not. I think the shear values are incorrect.

Look at the storms far to the north east as well - they have been torn apart leaving trails several hundred miles long in just a few short hours.

That is some pretty intense shear.

The values on the maps must be understated/incorrect.

I will take what I can see on satellite imagery over maps that have been wrong before.

We're expecting CIMSS to be correct. We know what we see on satellite imagery. The two do _not_ correspond with each other. Given the satellite is real time imagery - and the shear maps are computer generated overlays - I think there is no reason to trust the CIMSS maps right now.


That kind of shear your describing could be upwards to 30kts, and I know that would displace the center from the convection.
Member Since: Posts: Comments:
Quoting cloudburst2011:


i agree more like 20-25 kts right now ..

Does that men that he will be ripped apart soon?
Member Since: Posts: Comments:
Quoting P451:


Look at the condition of the system and the condition of the clouds to Don's north.

Look over the satellite imagery - different IR bands too - and you will see this 10 to 15 knots of shear is clearly wrong. It is MUCH higher.





If it was higher than 10-15 knots, the center would be exposed. Instead, the system is becoming better organized. It's not as high as you are advertising.

As I said before, the small size of the system makes it more susceptible to lower wind shear than larger systems can deal with.
Member Since: Posts: Comments:

Viewing: 321 - 271

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.