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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1342. MZV
It may not qualify as a pinhole eye ... but maybe a "knothole" could be justified.
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Any guesses for the pressure on the next center fix? I say 971 or 970.
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Quoting StSimonsIslandGAGuy:
No hurricane force winds found. Will this be a record deep tropical storm?



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,

Evidently the NHC saw Hurricane force winds. Its now a Hurricane.
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Quoting CybrTeddy:
Can't believe we're talking about another Hurricane Alex already.. has it really been 6 years since 2004?


I know exactly what you're feeling. Alex '04 was the first storm that I ever tracked.
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Quoting CosmicEvents:
That's right. Winds catch up to pressure drops. This cyclone is still too big to fully get itself wound up in relation to the pressure before it runs into land.


Exactly, but I think we will slowly see winds go up tonight. I'm looking at a Category 2 Hurricane at landfall.
Member Since: July 1, 2008 Posts: 13 Comments: 7436
Quoting JLPR2:


two it seems, how come we dont have a message thingy? XD


Sometimes when preliminary measurements are unbelievable, they end up having to confirm. In the case of Gilbert, I recall Jeff Masters relaying the pressure data to the NHC twice and the NHC had to confirm with another RECON plane.
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What exactly are dropsondes?
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AOI
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Quoting StormChaser81:


Low 900's, 904mb or something like that.

Wilma was 883mb

Rita was 897mb

Katrina bottomed at 902. Rita operationally was 897 but later analyzed to be 895. Wilma bottomed at at least 882 (NHC says it might have been lower in post storm analysis, but that's the official number).
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Quoting MiamiHurricanes09:
Things to note:

1) Alex has a very small compact eye.
2) Alex has a rather strong eyewall.
3) 2 dropsondes were dropped into the eye of Alex.

Very interesting night ahead of us...



Indeed. May see a sub 970 mb Hurricane tonight.
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1330. Patrap
.4

ALEX is a Large CV Cyclone and dosent need to Kow tow to any Pressure related obscure Category.

So there.

LOL
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Quoting Ameister12:
Call me a dunce and slap me silly if Alex isn't a hurricane by late tonight.


Why wait that long? jk
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If you are interested, StormW on with Barometer Bob.

wrbn on livestream.com. Broadcast Live Free
Member Since: September 2, 2009 Posts: 130 Comments: 21194



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That said, if Alex is now a Hurricane, then special advisory will be out in a few mins from NHC
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1325. primez
Quoting CybrTeddy:
Can't believe we're talking about another Hurricane Alex already.. has it really been 6 years since 2004?

I know, right? I first joined WU during the 2004 season. Have been lurking ever since. :)

Can't believe it's been 6 years.
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thats what it is son,not because they havent posted it doesnt mean it aint so
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Things to note:

1) Alex has a very small compact eye.
2) Alex has a rather strong eyewall.
3) 2 dropsondes were dropped into the eye of Alex.

Very interesting night ahead of us...

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Aaah - now I get it! Oy.
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1320. SLU
NB: Alex now becomes the 1st June hurricane in the Atlantic since Hurricane Alison in 1995 (65kts) and only the second June hurricane since Hurricane Bonnie in 1986 (75kts)

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1319. Patrap
The Graph is NOT a representation of any Given storm

And thats a Major Flaw in the SSS.

Thats why we have Separate Surge and Wind Warnings


Pressure isnt the Impact scale.

Winds and surge do the deed.

Not pressure
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1318. Max1023
EDIT: Second sonde showed 973 with 1 knot. FIrst one must have been dropped in the eyewall.
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Can't believe we're talking about another Hurricane Alex already.. has it really been 6 years since 2004?
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Quoting MiamiHurricanes09:
Alex now a hurricane.

AL, 01, 2010063000, , BEST, 0, 230N, 944W, 65, 974, HU,
Interesting. Well, there has to be HU force winds in there somewhere with those pressures, regardless. Or there will be very soon...
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting AustinTXWeather:


Take it that is low-? To put pressure in perspective for me, any idea what Katrina was?


Low 900's, 904mb or something like that.

Wilma was 883mb

Rita was 897mb
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StormW on air now central time.
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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.
That's right. Winds catch up to pressure drops. This cyclone is still too big to fully get itself wound up in relation to the pressure before it runs into land.
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1311. IKE
Quoting AustinTXWeather:


Take it that is low-? To put pressure in perspective for me, any idea what Katrina was?


902 mb's.

Looking at the visible floater, he looks like he's going south of west....Link
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Last storm with a compareable pressure was Ida from last year.

Bottomed out with a 975mb and 105mph
Link
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Quoting Baltimorebirds:
Rude people on the blog I tell ya.Any way did Alex just go through rapid intensifacation(or ri)


I wouldn't say rapid intensification but it did intensify rather quickly
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1308. Max1023
Dropsonde recorded 45 knot winds in the NW quad with 975mb pressure outside the eye/CoC. Essentially this confirms most of the SFMR readings, as the SFMR was reading 45 knots at the same place. All of those 60 knot readings in the SW quad are legit.

Also, if there is 45 knots of wind at 975 mb then the central pressure has to be under 971mb. The conversion is 1mb for every 10 knots of wind found when you are inside of the eyewall.
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Quoting jamesrainier:


Medium strength category 2 hurricane is what Alex should be.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
...bout time StormW is on the air !
BB was putting me to sleep..
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1304. TBPauly
Just got a pretty good downpour here in Pinellas Park...now seeing lightning to the west, sounding like it's building back towards me a little.
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1303. JLPR2
Quoting Stormchaser2007:
Recon put out a dropsponde in the eye.


two it seems, how come we dont have a message thingy? XD
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AustinTxWeather... Special K was 902mb
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Quoting AustinTXWeather:


Take it that is low-?


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Quoting Stormchaser2007:


With that pressure...

Alex should be at least a strong Cat 1.
Agree 100%.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
you know some times they issue a special advisory to upgrade a storm. They did it a few times last year wonder if they will do it this time seeing as it is so close to land ?
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Forecaster Franklin was just on TWC and said he was sure it was already a hurricane, just waiting on a wind reading to support it.

BTW, this is the first time I've ever gotten a face to put with the name "FORECASTER FRANKLIN" from NHC discussions, LOL.
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1297. SLU
084

WHXX01 KWBC 300034

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

0034 UTC WED JUN 30 2010



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



ATLANTIC OBJECTIVE AIDS FOR



TROPICAL CYCLONE ALEX (AL012010) 20100630 0000 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

100630 0000 100630 1200 100701 0000 100701 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 23.0N 94.4W 23.8N 96.3W 24.2N 98.3W 24.4N 100.5W

BAMD 23.0N 94.4W 23.5N 96.3W 23.9N 98.2W 23.9N 100.4W

BAMM 23.0N 94.4W 23.6N 96.3W 24.0N 98.2W 24.1N 100.4W

LBAR 23.0N 94.4W 24.0N 96.1W 25.2N 98.1W 26.3N 99.9W

SHIP 65KTS 74KTS 81KTS 80KTS

DSHP 65KTS 74KTS 81KTS 50KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

100702 0000 100703 0000 100704 0000 100705 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 24.5N 103.0W 25.5N 107.3W 26.8N 109.8W 28.1N 111.9W

BAMD 24.1N 103.1W 25.1N 107.7W 27.2N 110.8W 30.7N 112.0W

BAMM 24.2N 103.0W 25.2N 107.5W 27.1N 110.6W 29.5N 112.5W

LBAR 27.7N 101.7W 31.1N 104.0W 36.2N 102.1W 39.8N 95.2W

SHIP 77KTS 71KTS 60KTS 50KTS

DSHP 34KTS 27KTS 27KTS 27KTS



...INITIAL CONDITIONS...

LATCUR = 23.0N LONCUR = 94.4W DIRCUR = 280DEG SPDCUR = 9KT

LATM12 = 22.4N LONM12 = 92.7W DIRM12 = 312DEG SPDM12 = 11KT

LATM24 = 20.7N LONM24 = 91.6W

WNDCUR = 65KT RMAXWD = 15NM WNDM12 = 60KT

CENPRS = 974MB OUTPRS = 1006MB OUTRAD = 250NM SDEPTH = D

RD34NE = 150NM RD34SE = 150NM RD34SW = 75NM RD34NW = 125NM



$$

NNNN
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Quoting MiamiHurricanes09:
That's for sure, but what interests me is that I'm sure they'll find stronger winds than 65 knots.

A special advisory will likely be issued.


With that pressure...

Alex should be at least a strong Cat 1.
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Quoting MiamiHurricanes09:
That's for sure, but what interests me is that I'm sure they'll find stronger winds than 65 knots.

A special advisory will likely be issued.


Was just about to post that. Given its proximity to land, they'll probably get that out at quickly as they're certain it's a hurricane.
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Quoting Stormchaser2007:
Recon put out a dropsponde in the eye.
Newer one:

000
UZNT13 KNHC 300039
XXAA 80008 99230 70944 08234 99973 27601 03001 00746 ///// /////
92449 25601 32501 85194 22024 24002 88999 77999
31313 09608 80017
61616 AF303 1001A ALEX OB 07
62626 EYE SPL 2296N09436W 0019 MBL WND 02501 AEV 20802 DLM WND 36
001 972843 WL150 04002 084 REL 2296N09436W 001726 SPG 2296N09437W
001843 =
XXBB 80008 99230 70944 08234 00973 27601 11863 23002 22850 22024
33843 20839
21212 00973 03001 11856 27001 22843 21503
31313 09608 80017
61616 AF303 1001A ALEX OB 07
62626 EYE SPL 2296N09436W 0019 MBL WND 02501 AEV 20802 DLM WND 36
001 972843 WL150 04002 084 REL 2296N09436W 001726 SPG 2296N09437W
001843 =
;
Member Since: September 2, 2009 Posts: 130 Comments: 21194
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: 37860

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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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