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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Quoting AustinTXWeather:


Just getting back on > is Alex stalling?
We previously thought Alex was stalling but in reality it just slowed down in forward motion (considerably). Another thing to note is that Alex is no longer moving NW or WNW, but actually W.
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Quoting Patrap:
Last Night the P3 NOAA went Pfffttt and had to return on 3 Turning instead of 4.

Now tonight the HH AF C-130 returns for Mechanical.

I dont like the Trend.
Alex is a bad seed.

Mean Kid.

Sneakie.


I was thinking the same thing. What did that cane do?
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Quoting centex:
So it is nearly stationary. When stationary track does not mean much.


present movement...W or 280 degrees at 9 mph...
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Wow Pat you are under a Flood Watch untill Thursday Night.... Looks to be bad along the North Gulf Coast with very Heavy Rain and possible Water Spouts....

Taco :o)
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Quoting MiamiHurricanes09:
Why is the hurricane warning so lengthy from north to south when the hurricane force wind field is only 15 miles wide? There should be less red shading and more blue.



Without recon data they can only guess how large the hurricane windfield is.
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Quoting scott39:
Hypothetically, Just to make sure I understand, If a TC stalls and there is a weakness in the high pressure, it gravitates toward the weakness?


A stall happens for more than one reason. The steering winds can weaken to the N so that the storm has nothing to push or pull it one way or another. Alternatively, sometimes a system will start a motion in a particular direction and high pressure will build in above it to the N and block it making any further progress. It will then stall and creep to the Western edge of the high before lifting to the N again. Sometime the high is strong enough to force it onshore to the West such as is happening now with Alex.

A "weakness" in the steering is when you have light steering winds to the N of a system due to either a gap between two high pressure systems or an upper low retreating to the East and a high from the West lagging behind. This causes a " weakness" in the atmosphere and all storms want to go N as a natural tendency due to the rotation of the earth. If there is no high pressure to the N to force a storm West it will naturally try to make its way through the gap to the N and then recurve to the East.
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1935. Patrap
HH Flight Pattern for Data/Sonde drop




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Quoting atmoaggie:
I think you mean "I sure hope I never see anything like Tip in North America"...the gulf couldn't hold Tip...

Haha, funny, but true. :P
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Quoting angiest:


I think the center is still way out of radar range, and because you are looking very high up in the storm and through all the bands, its hard to see anything.


i figured there was an explantion. it was just too easy.
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Quoting Patrap:
The SMFR Failed just as they were starting the NE run


Which calls into question their earlier readings and the fact we had such strange ratio of pressure to surface velocity. Maybe the winds have been hurricane force since the last flight and we just didn't know it because SMFR was giving back bad data...
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Does anybody have information about the population, urban centers etc. that Alex is heading for in Mexico.
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Quoting MiamiHurricanes09:
Regardless of stalling a weakness attracts a tropical cyclone or area of low pressure. What stalling does is let other factors (such as troughs, ridges, etc...) happen without having an affect on the system which in turn changes the track greatly.


Just getting back on > is Alex stalling?
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The Mexican Navy has evacuated most inhabitants of the forecast landfall area...no messing around.
Member Since: August 14, 2007 Posts: 0 Comments: 435
Quoting mobilebayal:


Interesting facts about Hurricane Tip, 1900Hurricane. An amazing storm with an 870 sea level pressure and peak winds of 190mph. Thanks for sharing. I sure hope I never see anything like Tip in the Gulf!
I think you mean "I sure hope I never see anything like Tip in North America"...the gulf couldn't hold Tip...
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1927. aquak9
klink to pat
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Why is the hurricane warning so lengthy from north to south when the hurricane force wind field is only 15 miles wide? There should be less red shading and more blue.

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Quoting Orcasystems:


ROFL, its a lonely world out there :)


:P
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so it that the center at 5o'clock? if so, it's going south
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1922. USSINS
Quoting Patrap:
The SMFR Failed just as they were starting the NE run


Then I guess the NE run is part of their first pass through the eye.
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1921. aquak9
yo keeper!

no obviously I'm not happy about this, ok? but if it's gonna be crazy Season™ then I might as well be here for the official start.
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1920. angiest
Quoting truecajun:


I'm going to try to bump post so we can get some feedback on this.


I think the center is still way out of radar range, and because you are looking very high up in the storm and through all the bands, its hard to see anything.

EDIT; Maybe the last couple of frames the center does just come in. I am not booted into Windows atm or I would look at grlevel3.
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1918. Patrap
..Klink'
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Quoting HurricaneLovr75:
THE
SHIPS RAPID INTENSIFICATION INDEX SHOWS A 33 PERCENT PROBABILITY OF
RAPID INTENSIFICATION...I.E. A 30-KT INCREASE OVER 24 HOURS.
I'm still expecting a category 2 hurricane at landfall over Mexico.
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1916. guygee
Yeah looks to me like the center is just coming into view on long-range radar. Here is the a link to the long range NWS-BRO loop.
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Quoting truecajun:


oh darn. ritaevac, post it again. i don't know how to post images here. it's too far back for everyone to go back. they don't want to "miss" anything.

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1914. centex
So it is nearly stationary. When stationary track does not mean much.
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http://www.ssd.noaa.gov/goes/flt/t1/bd-l.jpg
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1912. Patrap
The SMFR Failed just as they were starting the NE run
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Quoting Patrap:
S Lowed from 13 to 9mph in forward speed.

Either angular Mo did that or somethings changed aloft.
Somethings definitely changed aloft. I'm quite eager to see what 03:00 UTC steering currents show.
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Quoting MrstormX:
Hmmm... I just realized I was the first person on this blog who posted the first "hurricane" advisory this year, and maybe the first "hurricane" discussion as well but I will have to look. Anyways that was a random speech, but exciting for me anyways lol


ROFL, its a lonely world out there :)
Member Since: October 1, 2007 Posts: 81 Comments: 26511
1909. USSINS
Hurricane Hunters' radar failed in the first pass through the eye last mission, but say another plane is headed there shortly.
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THE
SHIPS RAPID INTENSIFICATION INDEX SHOWS A 33 PERCENT PROBABILITY OF
RAPID INTENSIFICATION...I.E. A 30-KT INCREASE OVER 24 HOURS.
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Quoting truecajun:


I'm going to try to bump post so we can get some feedback on this.


oh darn. ritaevac, post it again. i don't know how to post images here. it's too far back for everyone to go back. they don't want to "miss" anything.
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1900. aquak9 9:43 PM CDT on June 29, 2010

Aww dangit, I missed my post again. That one had my name written all over it! XP
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972.9 mb pressure, winds 65-kt. That's quiet a low pressure from 980 mb at 8 PM. Is Alex's central pressure deepening quickly and winds about to ramp up even higher (I hope not)?
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Link

Nice
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Hmmm... I just realized I was the first person on this blog who posted the first "hurricane" advisory this year, and maybe the first "hurricane" discussion as well but I will have to look. Anyways that was a random speech, but exciting for me anyways lol
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Quoting RitaEvac:
Can you see the center at the 5'o clock angle on radar? looks to be moving SW and I know this would be way up in the top part of the clouds being so far off



I'm going to try to bump post so we can get some feedback on this.
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1901. KEEPEROFTHEGATE (Mod)
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1900. aquak9
1st cane of Season™, folks!

all lift drinks together! Cheers!
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So it really was based on Dvorak combined with the pressure and what obs the HH got. Reasonable, I suppose.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
On another note - this wave that is just exiting Africa, are any models developing it? I didn't see the GFS (regular one) developing it. Any others?

Thanks.
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Quoting Delsol:

So the ridge has weakened do you feel this is causing alex to stall? and will he head more north if the weakness is larger?
-
Man there really has been a windsheild wiper feeling to this storm... tracks trends more southernly by day and more north at night.
It has weakened some but not greatly.
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1895. Cochina
Quoting kidd5433:
Just got settled in at my hotel room in McAllen. Was in the same Hotel for Dolly so I thought for this trip I would stay in the same place. Not much going on right now just some showers passing by from time to time, busy day tomorrow as I have to hook up three 100kw generators and make a plan to survive the night.

I always appreciate all of the quality information on Masters-Blog. And I always find it a little entertaining reading the comment section.

.


I'm in McAllen~Edinburg too! (but that's where I live)
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1894. Patrap
S Lowed from 13 to 9mph in forward speed.

Either angular Mo did that or somethings changed aloft.
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1893. will45
I tell ya guys it looks like this year weaknesses arnt what they used to be
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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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