Tropical weather analysis - October 12, 2010

By: KoritheMan , 2:24 AM GMT on October 13, 2010


Hurricane Paula became a Category 2 hurricane early this afternoon. As of the latest NHC advisory (7:00 PM CDT), here is the latest information on Paula:

Wind: 100 mph, with higher gusts
Movement: N at 9 mph
Pressure: 981 mb
Location: 19.6°N 86.0°W
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Infrared satellite animations show that Paula is a very small but well-organized hurricane, with a well-defined poleward (north) and equatorial (west) outflow channels due to an amplifying upper trough currently moving across the deep south. However, outflow remains quite restricted to the east, and particularly to the south, due to 20 kt of southerly vertical wind shear analyzed by University of Wisconsin CIMSS. This shear is being induced by a well-defined mid- to upper-level ridge to the east.

An eye is not currently present using conventional satellite imagery, but it was earlier, and all indications are that Paula has maintained her strength over the last couple of hours.

Figure 1. Latest infrared satellite image of Hurricane Paula.

Doppler radar out of Cancun, Mexico shows that Paula has a very small eye, and earlier reconnaissance reports indicates that the eye is no more than, say, 10-15 miles wide. Indeed, if I hadn't been forecasting these systems for three years, I would not, as a layman, be able to readily tell just where Paula's eye is using the aforementioned radar imagery.

Figure 2. Latest still frame image from Cancun's doppler radar. Notice that the eye is not easily discernible on this image and as I said, even following the radar loop given above, the layman would very likely have a tough time identifying Paula's small eye.

I've never seen a Caribbean hurricane as small as Paula, except for perhaps Hurricane Iris in 2001, and even that's iffy since the latter had a larger radius of tropical storm force winds.

Steering analysis from CIMSS indicate that Paula is moving northward under the influence of the aforementioned anticyclone to the east.

Once this shear gets into the core, then rapid weakening is possible, given the hurricane's small size. Shear is forecast to gradually increase over the next 24 hours, and beyond that time, rapidly increase. However, shear should be light enough over the next 12 hours or so to allow a little more intensification of Paula. I will not go as high as the current NHC intensity forecast, however. Instead, I'll go up to 90 kt/105 mph, though it would not be surprising given current trends if Paula has already peaked.

After 24 hours, the shear will increase dramatically, as previously noted, and will also veer from southerly to southwesterly by 36-48 hours, and remain that way throughout the forecast period. This, combined with the likelihood of dry air entrainment from the Gulf of Mexico, along with interaction with the Cuban landmass, suggests that Paula may not even last five days as a tropical cyclone.

In fact, some of the models, including the reliable ECMWF, insist on losing Paula's circulation over the next 1-3 days or have a severely weakened tropical cyclone meandering in the northwest Caribbean Sea for several days, and this is a possible scenario. However, I feel that Paula will maintain enough vertical depth to feel the effects of the trough currently moving across the deep south.

One important development in the synoptic scale steering pattern that has transpired over the last 12 hours or so is that the aforementioned deep-layer trough and accompanying cold front has transitioned from a meridional flow to a more zonal one.

This is evident by analysis of water vapor imagery, mid-level steering from PSU's e-wall, and finally, CIMSS real-time steering data.

This suggests that Paula may move north for a little bit longer than was earlier anticipated, and as a result, I would expect a slight northward shift in the NHC forecast track at 11:00 PM. Nothing drastic, mind you, just a slight northward shift. South Florida is still very likely to avoid a landfall from this storm, and the Florida Keys probably will too. Nevertheless, interests in those areas should still monitor the progress of Paula closely over the next several days.

The current transition to a more zonal flow notwithstanding, Paula should still ultimately miss the US and generally follow the NHC's forecast track, since all of the global models foresee the trough reamplifying over the next day or two as it moves across the southeast United States.

Right now, I agree pretty strongly with the NHC's current forecast track, though I am a little bit further north of it after 24 hours and beyond:

Figure 3. Latest NHC 5-day forecast track for Paula.

Interests in the Yucatan Peninsula, the Cayman Islands, western and central Cuba, the Florida Keys, south Florida, and the Bahamas should closely follow the progress of Paula over the next several days.

In the meantime, heavy, flooding rains are possible across the eastern portion of the Yucatan Peninsula and western Cuba over the next day or two, along with the likelihood of sustained tropical storm force winds for the former and sustained hurricane force winds for the latter.

The eastern Yucatan Peninsula can expect sustained tropical storm force winds throughout the morning tomorrow, with western Cuba experiencing those winds Wednesday afternoon. Hurricane force sustained winds are likely across western Cuba Wednesday night and into Thursday morning.

Additionally, storm surge flooding will be a serious concern for those areas, as well.

Watches and warnings



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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3. Bordonaro
2:30 AM GMT on October 13, 2010
Nice job, and Paula is blowing up again!!
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2. Thrawst
2:29 AM GMT on October 13, 2010
Thanks Korithe :)
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1. MiamiHurricanes09
2:26 AM GMT on October 13, 2010
Thanks for the update Kori. Appreciated by me as usual.
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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