cieldumort
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Loc: Austin, Tx
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Hanna may have some characteristics that change the game today
Wed Sep 03 2008 03:27 AM
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Recall Saturday that Hanna very nearly was reclassified as a Subtropical Storm. The cyclone went from being a classic warm-cored tropical cyclone, to interacting with an upper-level low, and finally melding with the upper level low that day and night.
In response to interaction with the TUTT which had been impeding intensification, Hanna suddenly took on an appearance closely resembling that of a deep-layered, cold-core cut-off low. It is arguable that if it hadn't been for the northwesterly shear imparted upon it courtesy Gustav, Hanna would never have had so much very deep convection flaring up to the south and southeast... and subsequently, never had multiple center reformations to the southeast - and all would be good and well with forecasts insisting on an imminent northwesterly turn, but without those center reformations, Hanna could also have become a subtropical storm for at least a couple of advisories.
In the end, Hanna's LLC caught up with multiple rounds of extremely deep convection.. West Pac-style deep convection, even... and intensification was simply off to the races. But, as shear would have it, this was not to last.
And one now has to wonder how much that transition from tropical to (arguably) subtropical and back to tropical again really took.
The case for considering the possibility that Hanna is once again exhibiting a trend a bit back towards subtropical in nature is twofold:
First, a recent recon center fix, if correct, shows that Hanna may be attempting to turn into a cold-cored cyclone. By very definition, this would negate legitimately recognizing her as a Tropical Cyclone. Second, the strongest winds are no longer all right around the center of circulation, but also within a fuzzy band some 40-75 miles out from the center, based on the sampled portions of the windfield so far, suggesting some subtropical characteristics may be in play within the windfield. (This certainly isn't in well-developed rainbands in this region, as the rainbands are mostly all to her south and southeast (See Selected Recon Data Below)
The practical reason for considering Hanna partially still hanging on to subtropical traits is not merely in the interest of being correct, but such a consideration may actually have some implications for forecasting how the cyclone interacts with the environment around her. A subtropical cyclone might have more or less ability to withstand potential disruptions from land interactions, and in some cases, not react as detrimentally to shear, as two potentially relevant examples.
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 3rd day of the month at 05:39Z
E. Location of the Estimated Maximum Surface Wind: 65 nautical miles (75 statute miles) to the NNW (330°) of center fix
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 16°C (61°F) at a pressure alt. of 1,525m (5,003ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 12°C (54°F) at a pressure alt. of 1,524m (5,000ft)
Hanna is now hugging the extreme north Haitian coast. Pressures are falling all around this island, and most of the deepest convection has persisted over and to the south and southeast of the island for over twelve hours, while the center of circulation has continued to pull ever more to the south and/or east, over all, over time.
A potential fly in the forecast reasoning is becoming apparent, as the ease with which this cyclone takes on a few significant subtropical characteristics when not burying itself within deep thunderstorms, such that its surface circulation remains very intact and symmetrical if only a bit morphed, and to then jump into wherever the deepest convection has reappeared - and to then transform back into a deepening, warm-cored tropical cyclone, opens up the distinct possibility that its surface circulation may begin to wrap around Haiti.. maybe gels somewhere even south or east of there... into the new location of deepest convection.
This bit of an outlier possibility should be reconciled by this time tomorrow. If Hanna has not by then begun the forecast northwest movement, something is probably amiss in that call.
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