Tropical weather analysis - August 30, 3011

By: KoritheMan , 1:27 AM GMT on August 31, 2011


Tropical Storm Katia formed early this morning over the eastern Atlantic. As of the latest NHC advisory, here is the information on Katia:

Wind: 60 mph, with higher gusts
Location: 12.7°N 35.4°W
Movement: WNW at 20 mph
Pressure: 997 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Satellite loops show that the tropical cyclone is gradually becoming better organized. Upper-level outflow is excellent in the western quadrant, and is slowly improving in the east, implying a gradual reduction in the adverse northeasterly to easterly flow that was impacting it yesterday.

Figure 1. Latest infrared satellite image of Tropical Storm Katia, courtesy of NOAA's Satellite Services Division (SSD).

Atmospheric parameters appear conducive for additional strengthening, and I do expect that Katia will become our second hurricane over the next day or so. At longer ranges, it will also very likely our second major hurricane as well. The GFDL and HWRF take Katia up to major hurricane strength in about four days while it churns through the central Atlantic on a path several hundred miles northeast of the northern Leeward Islands.

The only impediment to development I can detect is a large area of subsidence over the central Atlantic between 60 and 50W. However, at most this will only quell potential for rapid intensification, and there is no reason to assume Katia will not become a powerful hurricane in about four days.

Katia is being steered by a large break in the central Atlantic subtropical ridge, associated with large scale troughing over the western Atlantic. However, the core of this weakness is rather far to the north, so Katia is unlikely to bend to the northwest until Sunday or Monday. Nevertheless, a gradual gain in latitude is likely given the persistent presence of the weakness, which is forecast to amplify eastward over the next several days.

The long-range model solutions continue to diverge, with the GFS and ECMWF along the eastern end of the model consensus, while the NOGAPS and CMC are farther south. Given that the former camp are usually reliable, especially when they are relatively harmonious, it is hard to go against them. However, given that large scale troughing has largely been overdone for most of the duration of this season, combined with the possibility of a more westward tug from a potential Gulf of Mexico tropical cyclone and Katia's fairly low latitude, I am inclined to be just a little bit south of those models, and recurvature is likely to be gradual, not sharp. Overall, my forecast track is in best agreement with the National Hurricane Center official one:

Figure 2. Latest NHC 5-day forecast track for Tropical Storm Katia.

Given the uncertainty in the eventual evolution of the emergent synoptic pattern over the Atlantic, interests in Bermuda should closely monitor the progress of this tropical cyclone, which will probably be a large and powerful hurricane at their latitude.

The northern Leeward Islands should also monitor it, but I would be surprised to see any appreciable impact to these areas outside of high surf and weak squalls on the south side of the circulation envelope.

Gulf of Mexico disturbance

We continue to monitor the potential for tropical troubles in the Gulf of Mexico. The global models continue to suggest that an area of disturbed weather, associated with a tropical wave moving through the western Caribbean, will manifest in the western or central Gulf of Mexico as this system interacts with a stalled frontal boundary across the northern Gulf. As of now, this system is producing only disorganized shower activity. However, surface observations suggest that a cyclonic circulation could be forming. However, surface pressures are still not really all that low, and there is evidence of westerly shear over the disturbance, so any development will be slow to occur in the near-term.

However, there are indications that the upper flow is gradually improving as the aforementioned frontal zone moves somewhat northward. Wind shear values are forecast to continue to slowly relax over the next several days as the disturbance moves west-northwest into the western Gulf of Mexico. Given a complex synoptic setup characterized by weak steering currents in the wake of central plains troughing, the ultimate trajectory of this system is uncertain. The GFS meanders it off the southeast coast of Louisiana late Friday into early Monday, while the CMC brings it into south Texas. Such discrepancy is usually a sign of a slow moving system.

All we can expect at this time is an area of disturbed weather to develop with a potential surface low trying to sneak underneath the convection as it meanders in an environment of weak synoptic steering. This is not uncommon of Gulf of Mexico development during this portion of the season.

Heavy rains could overspread large portions of the Texas and Louisiana coasts beginning late this week into next week.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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7. jazzie
3:11 AM GMT on August 31, 2011
Thanks for a great post man, I value your knowledge.
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6. cyclonekid
1:45 AM GMT on August 31, 2011
Gracias! Been a while since we've had a GOM storm. Last one was Don I believe. It'll be nice to see a little change in the tropics than just East Coast form-ers and Cape Verde TWs.
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5. MiamiHurricanes09
1:40 AM GMT on August 31, 2011
Thanks for the update Kori. Always appreciated.
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4. nolacane2009
1:38 AM GMT on August 31, 2011
Thanks for the awesome update.
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3. caneswatch
1:37 AM GMT on August 31, 2011
Thanks Kori!
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2. muddertracker
1:34 AM GMT on August 31, 2011
my favorite part is the "heavy rains for..texas" Great!
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1. aislinnpaps
1:34 AM GMT on August 31, 2011
Thanks, Kori,
I'll be watching as I can for what will happen with these.
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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