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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1393. Patrap
The Cat Number never means squat.
Been beating that dead Squid for 5 years.

Its the Wind Load and Surge that makes the Impact.

Always.



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primadonna... is it officially a hurricane? If so, please link your information.
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Quoting primadonnagirl:
alex is finally a cane!

Did the NHC upgrade it?
Member Since: January 24, 2010 Posts: 0 Comments: 27
Quoting clwstmchasr:
We are all looking at Alex on the satellite and pretty much figuring it is a hurricane and yet at the 8:00 advisory they kept it at a TS. In their comments they mentioned waiting for the HH.

What about the Pacific? They seldom fly planes but have no problem upgrading based on satellite. Why the difference?
Ooooo. Good question.
Guess they just want to use the best available, whatever that may be.
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Quoting Patrap:
ALEX has always been forecasted for days to Peak around 90Mph..considering his Girth and Expanse..thats a good solid forecast
Still iz.

This aint a Fluffy Cindy type Yucatan Bred Poofer.

Itsa the real McCoy stuck in June..late June


he is a shocker for late june
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I noticed Alex samed to move WSW in the last few loops, definitely a Mexico landfall now I'm thinking!
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alex is finally a cane!
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Quoting StSimonsIslandGAGuy:
I hope they keep it at tropical storm strength and don't find a surface wind near hurricane force. A record deep tropical storm would be pretty cool.

Do you think that even if the NHC couldn't find any hurricane force surface winds they would bump up Alex to hurricane strength because the NHC felt there HAD to be hurricane force winds in there somewhere?

I don't think they would do that. But never know.


They already have the ATCF file upgraded to hurricane.
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1383. Patrap
Quoting nrtiwlnvragn:


Suprised me the ones from the GIV took about 15 minutes.



Its a Long way down from 40K
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Quoting atmoaggie:
By Dvorak, I suppose? What other source could they have used to figure on 64 knots...outside of disbelief at 972 or 974 mb for a TS.


They also needed to get the data in for the model cycle and are probably pretty confident it is at least 65 knots.
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1381. angiest
Quoting 1900hurricane:

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).


Last advisory on Ike before landfall was 953mb.

Link
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Quoting MechEngMet:
MPH =~ knots x 1.1
Sooooo 65 knots x 1.1 =~ 71.5 mph
A "Knot" is a Nautical mile per hour, instead of the more common statute mile per hour.
Umm, in my world it is knot x 1.15
65 knot = ~74 mph
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1378. centex
Pressure can't keep falling and wind not follow.
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You don't really get a good eye till about 85 to 90 mph has been my experience.
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1375. Torgen
Looks like I tuned back in at the right time. Someone call StormW!
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Some further cloud top warming and new colder, deeper cell NE of center.

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MPH =~ knots x 1.1
Sooooo 65 knots x 1.1 =~ 71.5 mph
A "Knot" is a Nautical mile per hour, instead of the more common statute mile per hour.
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1371. Patrap
ALEX has always been forecasted for days to Peak around 90Mph..considering his Girth and Expanse..thats a good solid forecast
Still iz.

This aint a Fluffy Cindy type Yucatan Bred Poofer.

Itsa the real McCoy stuck in June..late June
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Quoting Baltimorebirds:
Okay what is 65 knots.Someone tell me please.

74.9 MPH around hurricane force.
Member Since: January 24, 2010 Posts: 0 Comments: 27
Quoting Stormchaser2007:
Alex's fix was SW of the 8pm advisory.

Alex does what he wants...


LOL. Watch it do a loop.
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Baltimorebirds... 65 knots would be approximately 75 mph. 1 kt= 1.15mph
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Quoting Stormchaser2007:
Alex's fix was SW of the 8pm advisory.

Alex does what he wants...
That can't be good.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1365. Max1023
Also the strongest winds have not been sampled, they are in the NE eyewall.
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1363. Patrap
Wamp wahhhhhhhhhhhhhhh......
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Quoting Patrap:
It aint ever a Hurricane till the NHC says its a Hurricane.

And that will be done if and when at the advisory..or a Special Before.

The watches and warnings are in Place.

YA chasing a rabbit in a Hat...

Bullwinkle

LOL
That data comes from the NHC file data server. Most things show up there, for the other NOAA agencies and entities, before they show on the usual webpage.
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Quoting Baltimorebirds:
Okay what is 65 knots.Someone tell me please.


74.75 mph, so 75 mph.
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1360. Patrap
00z Early Cycle NHC model tracks
Alex
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)





Dynamic Models (More sophisticated models)



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1359. MZV
Quoting angiest:
8nm wide eye? That is kinda small..


There is not good correlation between eye size and storm strength. I think Frances had a massive eye, 70 miles or so.
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1358. Max1023
1355 - 65 knots = 120km/hr and/or 75mph
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Alex's fix was SW of the 8pm advisory.

Alex does what he wants...
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Quoting atmoaggie:
Little GPS device that reports back to the plane the temp, dewpoint, and it's precise position every 0.5 seconds until it hits ground or water (though they sometimes fail halfway down.

Time to fall 4 - 6 minutes depending on conditions.


Suprised me the ones from the GIV took about 15 minutes.
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Quoting CybrTeddy:



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.
By Dvorak, I suppose? What other source could they have used to figure on 64 knots...outside of disbelief at 972 or 974 mb for a TS.
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Quoting Patrap:
It aint ever a Hurricane till the NHC says its a Hurricane.

And that will be done if and when at the advisory..or a Special Before.

The watches and warnings are in Place.

YA chasing a rabbit in a Hat...

Bullwinkle

LOL



Evening Pat
Think the NHC IS saying it's a hurricane. Just don't think they've told you yet.
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1351. angiest
8nm wide eye? That is kinda small..
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Member Since: September 2, 2009 Posts: 130 Comments: 21194
1349. Patrap
L. Eye Character: Open in the northwest


No fully developed Eyewall is Open to the NW..

So ALEX still hasnt built a Full Tower..
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1347. help4u
Watch this storm do a loop in the gulf.
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1346. Patrap
It aint ever a Hurricane till the NHC says its a Hurricane.

And that will be done if and when at the advisory..or a Special Before.

The watches and warnings are in Place.

YA chasing a rabbit in a Hat...

Bullwinkle

LOL
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Quoting Hurricanes12:
What exactly are dropsondes?
Little GPS device that reports back to the plane the temp, dewpoint, and it's precise position every 0.5 seconds until it hits ground or water (though they sometimes fail halfway down.

Time to fall 4 - 6 minutes depending on conditions.
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 30th day of the month at 00:40Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Storm Number & Year: 01L in 2010
Storm Name: Alex (flight in the North Atlantic basin)
Mission Number: 10
Observation Number: 05
A. Time of Center Fix: 30th day of the month at 0:17:20Z
B. Center Fix Coordinates: 22°57'N 94°23'W (22.95N 94.3833W)
B. Center Fix Location: 227 miles (365 km) to the ENE (77°) from Tampico, Tamaulipas, México.
C. Minimum Height at Standard Level: 1,191m (3,907ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 47kts (~ 54.1mph)
E. Location of the Estimated Maximum Surface Wind: 6 nautical miles (7 statute miles) to the WNW (293°) of center fix
F. Maximum Flight Level Wind Inbound: From 21° at 52kts (From the NNE at ~ 59.8mph)
G. Location of Maximum Flight Level Wind Inbound: 7 nautical miles (8 statute miles) to the WNW (297°) of center fix
H. Minimum Sea Level Pressure: 973mb (28.73 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 20°C (68°F) at a pressure alt. of 1,521m (4,990ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,523m (4,997ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Open in the northwest
M. Eye Shape & Diameter: Circular with a diameter of 8 nautical milesN. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1.5 nautical miles
Remarks Section:
Maximum Flight Level Wind: 52kts (~ 59.8mph) in the northwest quadrant at 0:15:10Z
Maximum Flight Level Wind Outbound: 60kts (~ 69.0mph) in the southeast quadrant at 0:19:30Z

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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.