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Tropical Update: September 4th; 6:20p.m EDT
By: MiamiHurricanes09 , 22:22 GMT le 04 septembre 2011
After going through a period of rapid intensification this morning, it appears Katia's intensity has leveled off. Latest conventional infrared satellite images depict an occluded eye feature. The reason that the eye is not too well-defined on satellite imagery is likely due to the constant updrafts that the cyclone has been firing in it's eyewall, causing for the overshooting tops to penetrate into the the eye. The latest intensity estimates from TAFB and SAB are a unanimous T5.0, however, over the past hour, ADT's Final-T number has been rising steadily due to cooling cloud tops in the cyclone's CDO and a warming eye feature.
The cyclone is currently moving towards the northwest under the influence of the southwestern periphery of the subtropical ridge. Model guidance suggests that the cyclone should continue to move in this general direction over the next 72 hours or so. An upper-level cyclone is forecast to develop in the general vicinity of 32˚N-37˚N and 80˚W-85˚ in about 84 hours, which should induce a meridional flow across the western Atlantic, and thus force the cyclone to make a poleward turn. The latest batch of models all suggest a recurvature in between the island of Bermuda and the eastern seaboard...and at this point in time, this appears to be the most likely track scenario. Nevertheless, the aforementioned areas are encouraged to follow the progress of Katia.
Atmospheric conditions appear conducive for further strengthening over the next 48 hours, save the low mid-level relative humidity values, and it appears likely that Katia will become the season's second major hurricane. Due to the fact that the cyclone will probably still have another 2-3 days of favorable to marginally favorable atmospheric conditions, it is possible that Katia could even make a run at category 4 status, albeit somewhat unlikely. Beyond 72 hours, a cooling sea surface, and warming upper-level atmosphere (as noted in the 5p.m discussion, which is just fancy talk for a more stable environment) should all allow for gradual weakening.
The main threat from Katia will likely only be rip currents, unless the track changes considerably towards the left or right.
Figure 1. Aqua MODIS visible satellite image of Hurricane Katia valid 14:45UTC, or 10:45a.m EDT.
Tropical Storm Lee
There isn't much to say about Lee. It continues to dump heavy rainfall over the southeastern United States as it meanders northward under the influence of a shortwave trough that continues to dig southeastward as noted on water vapor imagery. During the next few hours the cyclone should start to turn towards the northeast or east-northeast due to the a progressively changing steering regime courtesy of the aforementioned shortwave. A piece of this shortwave is forecast to split, interact with Lee's circulation, and then later be absorbed by a frontal system causing for an extratropical transition. The main threat from Lee is, and will continue to be, heavy rainfall over the next few days.
Global models have been hinting at some possible development from some energy that Lee may leave behind in the Gulf of Mexico. This area will be watched carefully as the GFS, CMC, and NOGAPS all hint at some sort of tropical development.
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