Alex building an eyewall, still not a hurricane

By: Dr. Jeff Masters , 7:34 PM GMT on June 29, 2010

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Tropical Storm Alex is slowly building an eyewall, which is now more than 50% complete, according to recent satellite imagery and microwave images (Figure 1.) Satellite loops show a slot of dry air is spiraling into the center of the storm, and until this dry slot gets closed off, Alex will not be able to intensify significantly. Alex's heavy thunderstorms and low level spiral bands continue to slowly increase, but upper-level outflow is mediocre to the north and east, and absent elsewhere. The Hurricane Hunters are in the storm and have not found any hurricane-force winds at the surface yet.


Figure 1. Microwave "radar in space" image taken at 10:11 am CDT Tuesday June 28, 2010, showing that Alex had built an eyewall a little more than 50% complete. Image credit: Navy Research Lab.

Impacts
Alex is already bringing bands of heavy rain to the coasts of Texas and Mexico, as seen on the Brownsville, Texas radar. Hurricane local statements with projections for how Alex will affect the coast are now being issued by the National Weather Service in Brownsville and Corpus Christi. Since Alex is a large storm, it will have a storm surge that will affect most of the South Texas coast. NHC is giving a 40% - 60% chance of a storm surge of at least 3 feet affecting the Brownsville area, and 10% - 30% chance the surge will exceed 5 feet. In theory, a Category 2 hurricane moving WNW at 5 mph can bring a storm surge of up to 8 - 9 feet to the South Texas coast (Figure 2.) However, Alex is now unlikely to get that strong, and the surge should be less. Flooding damage from the expected 6 - 12 inches of rain from Alex will also be a major concern, as will wind damage. The combined wind, surge, and flooding damage from 2008's Hurricane Dolly, which hit near Brownsville, were about $1.05 billion. Dolly was a Category 2 hurricane offshore that weakened to a Category 1 hurricane with 85 mph winds when it made landfall. I expect Alex will be similar in its impacts to Dolly, though Alex's storm surge damage is likely to be greater. If Alex hits more than 50 miles south of the Texas border, as currently appears likely, the damage will be far less, since this region of the coast is relatively sparsely populated.


Figure 2. Maximum Water Depth (storm tide minus the elevation of the land it is passing over) computed using the primary computer model used by the National Hurricane Center (NHC) to forecast storm surge--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The accuracy of the SLOSH model is advertised as plus or minus 20%. The "Maximum Water Depth" image shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of five feet above mean sea level, and the combined storm surge and tide (the "storm tide") is ten feet at your location, the water depth image will show five feet of inundation. This Maximum of the "Maximum Envelope of Waters" (MOM) image was generated for high tide, and thus shows the worst-case inundation scenarios for a mid-strength Category 2 hurricane moving WNW at 5 mph. For more information on storm surge, consult our detailed storm surge pages.

Track forecast for Alex
The latest 12 UTC (7am CDT) runs of our most reliable computer models confirm the faster movement of Alex to the coast, and residents in the affected areas now have 12 hours less to prepare for Alex's arrival than it seemed with yesterday's forecasts. Conditions will begin to deteriorate along the coast late tonight, so today is the day to finish preparations if you live near the Texas/Mexico border! The ridge that is steering Alex to the northwest is expected to strengthen today and Wednesday, which should push Alex on a more west-northwest and then westerly track on Wednesday. A few models even have Alex moving west-southwest by the time it makes landfall. The most northerly landfall location, near Brownsville, is predicted by the HWRF model.

To get the probability of receiving tropical storm force winds or hurricane force winds for your location, I recommend the NHC wind probability forecasts. The 4am CDT (9 UTC) wind probability product predicted that Brownsville, Texas had the highest odds of getting a direct hit from Alex:

Brownsville, TX: 88% chance of tropical storm conditions (winds 39+ mph), 23% chance of hurricane force winds (74+ mph). This is the cumulative probability through Saturday morning. The wind probability forecasts also include separate probabilities for each 12-hour period between now and three days from now, and each 24 hours for the period 4 - 5 days from now.

Corpus Christi, TX: 42% tropical storm, 1% hurricane.

La Pesco, MX: 37% tropical storm, 3% hurricane.

Freeport, TX: 18% tropical storm, 0% hurricane.

Tampico, MX: 14% tropical storm, 0% hurricane.

Galveston, TX: 13% tropical storm, 0% hurricane.

Intensity forecast for Alex
Alex is over a region of ocean with a warm, clockwise rotating Loop Current eddy that broke off from the Loop Current in July 2009 and moved west-southwest over the past 11 months. This eddy has moderately high total ocean heat content . Wind shear has fallen to a low 5 knots, and is projected by the SHIPS model to remain in the low range, below 10 knots, this afternoon and Wednesday. The combination of low wind shear and moderately high ocean heat content should allow Alex to intensify into a Category 1 hurricane, but time is running out for it to be a Category 2 hurricane. NHC is giving Alex a 79% chance of being a hurricane on Wednesday morning, and a 4% chance it will be a major hurricane at that time. Water vapor satellite images show the amount of dry air over the western Gulf of Mexico has decreased over the past day, though as I noted above, the dry slot wrapping into Alex's core is currently keeping the storm from closing off an eyewall. Dry air may turn out to be an increasing detriment to Alex on Wednesday as the storm approaches land. Another factor limiting Alex's intensification may be that the atmosphere is more stable than usual right now--temperatures at 200 mb are a rather warm -50°C, and are expected to warm an additional 1 - 2 degrees by Wednesday. I don't expect Alex to stall out again, so slow motion leading to upwelling of cold water will probably not be a problem for Alex. The main issue limiting intensification will be the fact that Alex is so large, and it takes more time for a large storm to organize. Thus, I think Alex has only a 10% chance of intensifying into a major hurricane before landfall.

Elsewhere in the tropics
The last few runs of the NOGAPS model have been predicting the formation of a tropical disturbance off the coast of Nicaragua on Friday or Saturday that will move northwestward towards western Cuba. The GFS model, and the two models that use it for starting conditions, the GFDL and HWRF, are indicating the possibility that a weak extratropical storm may form along coastal Alabama this weekend. It is unlikely that such a storm would be over water long enough to transition to a tropical storm.

Wind and ocean current forecast for the BP oil disaster
It currently appears that Alex's winds will not directly affect the oil slick location. However, because Alex is such a deep low pressure region, strong southeast to south winds of 10 - 20 knots will blow over the oil slick region today through Thursday, according to the latest marine forecast from NOAA. The resulting currents should act to push oil to the west and northwest onto portions of the Louisiana, Mississippi, and Alabama coasts, according to the latest trajectory forecasts from NOAA and the State of Louisiana. Oil will also move westward along the central Louisiana coast towards the Texas border. Alex is currently bringing swells of 3 - 4 feet to the coastal regions impacted by the oil slick, and these swells will increase to 6 - 8 feet on Wednesday. Wave heights will increase to 5 - 7 feet on Wednesday. Alex is expected to bring a storm surge of 1 - 2 feet along the coast in the oil spill region. The swells and waves that will accompany these high water levels will act to push oil deep into the marshlands in some locations. The long range forecast for the oil slick region is uncertain, due to the possibility a weak area of low pressure might develop late this week along the remains of a cold front draped across the region.

Resources for the BP oil disaster
Map of oil spill location from the NOAA Satellite Services Division
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA's interactive mapping tool to overlay wind and ocean current forecasts, oil locations, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. Some topics I'll cover today on the show:

1) Alex
2) A look ahead at what may happen the rest of hurricane season

Today's show will be about 45 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Next post
I'll have an update Wednesday morning by 9:30am CDT. Rob Carver is planning on doing a late-night update tonight.

Jeff Masters

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1293. IKE
Quoting reedzone:
A comment here based on past storms... When pressure drops, the winds go up afterwards near what the pressure of the storm would be. Am I right, please correct me if I'm wrong.


True...the winds will respond. I feel sorry for those near where this crosses. I would be seeking a safe place to get to.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


Wasn't expecting that....wow.


Take it that is low-? To put pressure in perspective for me, any idea what Katrina was?
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Recon put out a dropsponde in the eye.
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1290. Patrap
Awaiting the new Pkg from ATCF

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Quoting Stormchaser2007:
Hurricane Alex at 11pm

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU, 64, NEQ,
That's for sure, but what interests me is that I'm sure they'll find stronger winds than 65 knots.

Regardless, a special advisory will likely be issued.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Wow I have been trying to see if we have ever had
a storm that was not a Hurricane and had a
pressure of 972mb......
Just to let you know I thought this was a Hurricane
this AM.... All I can say is "Wow"

Taco :o)
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What is that Titoxd... showing HU on the obs, huh? Wait til they make it official... the blog is gonna light up big time, even more that what it is!
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Quoting RitaEvac:
I will wet myself if it starts to ride south along the 95 longitude

its not going south its moving nearly due west towards Mexico
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The reason the pressure dropped so quickly is because you the tube (eyewall) with a void in it with down drafts in the inner eye and updrafts in the eyewall. Once the void(hole in eyewall) is filled its forcing the air down very quickly. With this being such a big storm it has aloft more forces going around it, making lots more down force in the eyewall.

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65kt with a 972mb?
Member Since: May 21, 2006 Posts: 5091 Comments: 115239
Quoting Titoxd:
From the running best track:

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU, 64, NEQ, 15, 15, 15, 15, 1006, 250, 15, 0, 0, L, 0, , 0, 0, ALEX, D,


Hurricane Alex has arrived.
Member Since: July 8, 2005 Posts: 259 Comments: 24179
1281. IKE
Looks like an upgrade.

That will make it....1-1-0, so far.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
A comment here based on past storms... When pressure drops, the winds go up afterwards near what the pressure of the storm would be. Am I right, please correct me if I'm wrong.
Member Since: July 1, 2008 Posts: 13 Comments: 7396
1279. Patrap
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Quoting Levi32:
Guess what guys.....ECMWF absolutely nailed this storm. Major cudos to that model in the face of the big-hitter GFS and CMC ensembles completely disagreeing with it for all this time, and now we have a clear winner. ECMWF was stellar and solid from the moment it shifted all the way west many many days ago, and despite being the southern-most outlier, it won out, clear-cut.
I haven't read the blog past this point made awhile ago, but it's a good point that bears repeating anyway. I don't know if the official stats would say so.....but I find that most years there's one model that seems to be in the groove, and it can last the entire season. It's definitely worth noting that so far, the EURO seems to be in the zone. Personally, that's the one that I'd be most concerned about if it was pointed my way. In previous years, it was the GFDL that had that spot, for me.
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Wonder how many Marcos you could put in Alex?
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Hurricane Alex at 11pm

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU, 64, NEQ,
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Alex now a hurricane.

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU,
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1274. KEEPEROFTHEGATE (Mod)
Quoting Tazmanian:
we may have a eye it may be so small we this cant see it
yep could be so small even smaller than a pin hole eye
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1273. Patrap
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Quoting dsenecal2009:
980mb and still a TS, good lord...it's like we swapped the Atlantic with the Pacific.


972.9 to be specific.
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1271. angiest
Man Alex is Ike's little... big... um... some kind of brother.
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1270. Titoxd
From the running best track:

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU, 64, NEQ, 15, 15, 15, 15, 1006, 250, 15, 0, 0, L, 0, , 0, 0, ALEX, D,
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Currently Alex is deeper than all but 2 of last years storms.
Member Since: July 8, 2005 Posts: 259 Comments: 24179
1267. Patrap
Quoting IKE:
Winds have to be hurricane force with that pressure.




The Size of the Cyclone isnt going to allow for the Pressure falls to react Like in a much smaller organized system.


Itsa Big Mutha..

Its all relative.

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1266. IKE
Quoting Patrap:
Looks Like a Good Center Fix

22.950N

94.400W


Moving south of west? 23.2N on the earlier advisory.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Yeah Savannahstorm... scary thought. Especially with a pressure drop like that!
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Quoting dsenecal2009:
980mb and still a TS, good lord...it's like we swapped the Atlantic with the Pacific.


Recon found 973.

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1263. KEEPEROFTHEGATE (Mod)
01L/TS/A/XX
MARK
22.9N/94.5W


POINT OF IMPACT 23.4N/97.8W
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SFMR winds of 62 knots and not contaminated. Alex definitely has an eyewall because winds are calm right over the COC and then really pick up when they get out of it.

000
URNT15 KNHC 300026
AF303 1001A ALEX HDOB 17 20100630
001700 2257N 09424W 8429 01265 9733 +207 +167 003008 011 022 000 00
001730 2257N 09424W 8429 01265 9729 +211 +168 211003 007 018 000 00
001800 2257N 09424W 8429 01265 9730 +212 +167 207012 016 016 000 03
001830 2256N 09418W 8429 01268 9737 +208 +170 204022 026 032 010 00
001900 2255N 09417W 8428 01278 9755 +188 +175 211032 037 999 999 03
001930 2254N 09416W 8439 01283 9778 +176 +175 213057 061 061 031 03
002000 2253N 09415W 8432 01302 9798 +173 +170 216058 060 062 030 00
002030 2252N 09414W 8445 01310 9820 +172 +166 216058 061 059 021 00
002100 2251N 09413W 8424 01346 9833 +173 +160 218053 054 051 013 00
002130 2251N 09413W 8424 01346 9838 +190 +154 221051 051 048 011 00
002200 2249N 09410W 8430 01359 9845 +195 +152 221048 050 044 003 00
002230 2247N 09409W 8429 01366 9851 +196 +155 226044 045 046 010 00
002300 2246N 09408W 8432 01367 9868 +173 +158 233049 052 055 023 03
002330 2245N 09407W 8438 01368 9876 +171 +162 228049 050 054 024 03
002400 2244N 09405W 8426 01380 9879 +171 +164 224048 050 060 037 03
002430 2243N 09404W 8426 01388 9887 +170 +162 224046 047 057 027 03
002500 2242N 09403W 8440 01380 9894 +167 +160 223052 054 052 023 00
002530 2240N 09402W 8415 01411 9894 +177 +157 220049 051 056 022 00
002600 2239N 09401W 8437 01394 9897 +186 +156 224051 053 047 010 03
002630 2238N 09359W 8429 01407 9900 +189 +159 223049 050 042 001 00
$$
;
Member Since: September 2, 2009 Posts: 130 Comments: 21194
When they do a go around at the COC again we might drop a few more mb. Crazy stuff
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980mb and still a TS, good Lord...it's like we swapped the Atlantic with the Pacific.
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1258. IKE
Winds have to be hurricane force with that pressure.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1255. Patrap
Looks Like a Good Center Fix

22.950N

94.400W
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we may have a eye it may be so small we this cant see it
Member Since: May 21, 2006 Posts: 5091 Comments: 115239
Tonight could be interesting.

Could drop "da chalupa"
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TropicalStormAlex heading toward (Tropic of Cancer) Mexico landfall in 19hours
(Straightline projection using its last 2 positions. Take with HUGE grain of salt)

Copy&paste TAM, MOB, PBI, SAL, 22.7N93.1W, 22.9N93.6W-28.7N88.4W, 23.2N94.0W-28.7N88.4W, 23.2N94.5W-28.7N88.4W, 23.2N94.0W-23.2N94.5W, 23.2N94.5W-23.2N97.8W into the GreatCircleMapper.

The shortest red line shows the heading between the last two positions. Below the map shows:
TSAlex had a heading of 270.1degrees (West), while
traveling a distance of 32miles (~56kilometres) over 3hours at a speed of ~11mph (~18kph);
and was 210miles from the Mexican coast in the direction it was heading.

* DeepwaterHorizon is marked at 28.7N88.4W
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1251. Patrap
Womp..wahhhhhhhhhh


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1250. Titoxd
Quoting Patrap:


That would be the Eye,or center where the Lowest Pressure would be found.

Its da middle


That is my point precisely; Alex has no visible eye in VIS imagery, so I was a bit surprised by the low wind speeds underneath the CDO...
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1249. will45
59.9 knots (~ 68.9 mph)
Tropical Storm
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Recon never saw winds above 55 knots the entire day, NHC strengthened it up to 70 mph. They'll likely make it a Hurricane shortly with the 61 knot winds.
Member Since: July 8, 2005 Posts: 259 Comments: 24179
I will wet myself if it starts to ride south along the 95 longitude
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Quoting ecflweatherfan:
001930 2254N 09416W 8439 01283 9778 +176 +175 213057 061 061 031 03
002000 2253N 09415W 8432 01302 9798 +173 +170 216058 060 062 030 00

Winds over 60 kts...


...and those readings are on the SE side of the COC. Just wait until they get into the NE quadrant.
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Quoting Patrap:


That would be the Eye,or center where the Lowest Pressure would be found.

Its da middle


Hahaha...
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1243. IKE
Quoting MiamiHurricanes09:
New minimum pressure 972.9mb!


Wasn't expecting that....wow.
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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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.