Intensifying Hermine closes in on the Texas/Mexico coast
Steadily intensifying Tropical Storm Hermine is closing in on the coast near the Texas/Mexico border, and should move ashore late tonight. Hermine became a tropical depression at 11pm last night, and could become a minimal hurricane by 11 pm tonight. Hermine's rate of intensification from nothing to a strong tropical storm is one of the fastest on record. It turns out that the extreme southwestern Gulf of Mexico's Bay of Campeche, where Hermine formed, is prone to these sort of rapidly intensifying tropical storms. The curvature and topography of the land help induce a counter-clockwise spin to the air over the region, which helps get tropical storms spinning up unusually quickly. Helping the spin-up process are the very warm 30°C waters, low 5 - 10 knots of wind shear, and moist atmosphere. Hermine promises to be a very wet storm, and latest long range radar out of Brownsville, Texas shows a large area of heavy rain has been drenching southern Texas and northern Mexico all afternoon, with radar estimated rainfall amounts exceeding two inches in a few areas along the coast. Radar loops show that an eyewall is attempting to form, but a region of dry air from over land spiraled into Hermine's core between 4 - 5pm EDT, disrupting eyewall formation. However, it now appears that Hermine has closed off its eye from this dry air, which should aid in intensification. Satellite imagery shows Hermine has vigorous thunderstorms with very cold tops, and improving low-level spiral banding.
Forecast for Hermine
Hermine doesn't have much time over water before it comes ashore, which is a good thing. The storm is steadily organizing, and has a shot at reaching hurricane strength before the center moves ashore late tonight, near midnight. Heavy rain will be the main threat from Hermine, though isolated tornadoes may also cause damage, particularly over South Texas. Hermine is expected to accelerate through Central Texas Tuesday and Wednesday, and the storm's rains will help alleviate moderate to severe drought conditions affecting Central Texas.
Figure 1. Late afternoon radar image of Tropical Storm Hermine. Note the band of dry air spiraling into the core of the storm from the north.
Gaston continues to suffer from dry air
An Air Force Hurricane Hunter aircraft spent the afternoon in Gaston's remains, and found a weak 1012 mb center of low pressure with only a limited region of westerly winds on the south side of the center of circulation. Top surface winds uncontaminated by heavy rain seen by their SFMR instrument were in the 30 - 35 mph range. The airplane found plenty of dry air in the storm's environment, and there are not enough heavy thunderstorms in ex-Gaston's circulation for it to qualify as a tropical depression. The remains of Gaston are now approaching the northern Lesser Antilles, and residents can expect a few heavy rain showers and wind gusts up to 40 mph beginning early this evening and continuing into the night. Latest radar out of Martinique doesn't show much in the way of heavy rain, and satellite imagery confirms that the thunderstorm activity associated with Gaston's remains is quite sparse. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops.
Figure 2. Afternoon satellite image of the remains of Gaston, approaching the Lesser Antilles Islands.
Forecast for Gaston
There is little change to the forecast for Gaston's remains. Dry air will continue to be the major impediment to development, and the system is unlikely to become a tropical depression today. However, wind shear, which is currently a moderate 10 knots, is forecast by the latest SHIPS model run to fall very low, 0 - 5 knots, tonight through Wednesday. With almost no wind shear affecting it, Gaston will a better chance of keeping the moisture from its heavy thunderstorms near its core on Tuesday. This will insulate the storm from the dry air surrounding it. The atmosphere is also moister in the eastern Caribbean, further increasing the chances of development. I believe it is probable Gaston will become a tropical depression again on Tuesday. NHC is currently giving Gaston a 70% chance of developing into a tropical depression by Wednesday, which is a reasonable forecast.
Heavy rain showers and gusty winds from the storm will affect Puerto Rico Tuesday morning through Wednesday afternoon. This activity will spread to the Dominican Republic Tuesday afternoon through Thursday morning. Assuming dry air and an encounter with Hispaniola's high mountains do not destroy Gaston, heavy rain from the storm should move over Haiti, eastern Cuba, and Jamaica Wednesday night and Thursday morning. The models don't give much support for Gaston surviving past Wednesday. The ECMWF, GFS, NOGAPS, Canadian, and HWRF models all dissipate Gaston. However, two models--the GFDL and UKMET--predict that Gaston will survive the dry air and an encounter with Hispaniola, and pass far enough south of the island to find a favorable environment in the Central Caribbean for development on Wednesday. Wind shear will be low, water temperatures will be hot, and the atmosphere will be plenty moist. Gaston could intensify into a hurricane in the Western Caribbean by the end of the week, as predicted by the latest run of the GFDL model.
Elsewhere in the tropics
The models are fairly unanimous in predicting development late this week of a tropical wave expected to emerge from the coast of Africa on Tuesday or Wednesday. The next storm will be called Igor.
Next post
I'll have an update in the morning.
Jeff Masters
Reader Comments
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AOI
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TS BUSTED FORECAST ALIBI
With that being said, please pass the tobasco.
I really didn't expect anything to develope when I was looking in that area Friday. Live and learn!
sometimes "Instinct" counts for a lot
Oh I was refering to my inattentiveness...I wrote her off Friday evening...of course I was looking forward to wonderful weather for the long weekend here in South Louisiana
Let go Orca! Let go...
ROFLMAO, I am willing to... its the darn models that keep it alive. One set says... nada... others say... TS... and three respected models including the SHIP say anywhere from a CAT 2- 4
That does not seem the case. If the conditions are right, all tropical cyclones can develop upper level anticyclones. Tropical Storm Hermine (and many others) developed its own upper level anticyclone. When a tropical cyclone has strong surface convergence with virtually no wind shear above it, it will positively create its own upper level ridge. Sometimes mere intense convection activity at the surface can generate an upper level anticyclone.
A tropical cyclone's upper level ridge can also be enhanced by diffluent flow aloft from the eastern side of an upper level low. The curving diffluent air increases winds at the periphery of the upper level high. If a tropical cyclone is under too much shear, the upper level high will be negligible or displaced from the center. Overall, upper level anticyclogenesis depend on the environment.
ACE is simply the best metric yet devised for measuring the accumulated energy spent over he course of a season, and as such it is very effective at detailing overall activity. I suppose that, for some, body counts and dollar amounts are a more effective measure, but from a meteorological point of view, ACE works quite well. To put it another way, while the devastating impact of a short-lived and powerful storm like Camille means more to the general population--that is, normal folks, journalists, insurance adjusters, and the like--its relatively low ACE says nothing much about the overall power of a particular season.
(Yes, ACE-wise, 2007 was low-normal...but half its total ACE came from one storm--Dean. This year's short-lived Alex was more energetic than 12 of that year's 14 mostly weak systems. When making year-to-year comparisons on which a season's "bustedness" is based, ACE works.)
Checking in from the Beautiful Island of Key West....
Had a wild Storm last night but was kinda cool looking over the water with the light show....
I see we had Hermine last night and explains why we had winds moving to the west....
well now we need to see what Ex-Gaston does and the new wave moving into the Atlantic....
Taco :o)
IKE:
Take a look
http://www.comoestaeso.com/forums/content.php?23-Live-Ocean-Park-Camera
Cloudly with 8KT winds, good for board padling
I do like ACE personally, so not disputing its worth. Its significance as an indicator of activity really does depend on what you define as activity. ACE, by its very nature, will often put more into the 'long trackers' than numbers. In terms of activity being what the CSU would call 'hurricane days', then yes, it is a fine determinant.
However, if activity is defined by the quantity of storms (which for most it is), it is far less clear cut. There are numerous examples of seasons which have fewer numbers in all three categories - Storm, Hurricane, Major - yet have higher ACE due to that season's propensity to/reliance on an active Cape Verde season.
That explains why i slept in until 10 this morning, lack of sun to wake me up, LOL (I'm in NRH)
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