SPECIAL UPDATE: TS Debby Weaken’s But Severe Thunderstorm Risk, Further Flooding Remains (Includes Video Update!!)

Image courtesy of NOAA

Well, Debby has weakened from a 60 to 50 mph storm and is looking rather unimpressive due to the amount of dry air working into the storm as well as the strong shear which is displacing ther bulk of her convection well off to the east. In fact the majority of the convection is actually out over the Atlantic with just narrow bands of thunderstorms over Florida.

Dry air and shear may be saving grace in avoiding catastropic flooding

As dry air continues to feed and wrap around Debby’s circulation, choking off vital convection around the centre, this does appear to be reducing the amount of rains we have seen so prevalent over the past 48 hours across much of Florida. Had this dry air not been entraining in or had the upper low to the west now blown much of the storm’s convection, now out over the Atlantic, we may have seen over next 48 to 72 hours another Allison. That was a storm which stalled around Houston for several days and produced as much as 36 inches of rain over Houston.

Yesterday alone we have seen an impressive 10.34 inches at St Petes, this is largely due to the deep tropical converyor which extends well out into the central, even southern Gulf which crossed the warm rich Gulf water, picking up vast amounts of moisture which simply trained onshore for many hours. The lack of movement in the system meant the same areas continued to see the never ending heavy rains.

This piling up of wind, rain and heavy seas via this conveyer have and continue to push 10-15 foot waves onshore on top of a 3-4 foot surge which is flooding many coastal areas along the west coast. Winds are blowing 20-30 mph with higher gusts.

Notice in the latest satelite image above how most of the deep convection is off Florida’s east coast. Also notice in the below visible image how the core of the storm is largely naked, void of any real convection, this is due to the dry air which has been streaming into the northwest of the storm off the US and has been choking the storm.

We saw multiple tornadoes touchdown, especially over central areas of Florida near Orlando yesterday. Dry air has a tendency to raise the tornado threat and it’s as these bands sweep across Florida from the storm they come up against varying winds and thus the thunderstorms embedded within these banding features start to rotate and can spin up brief tornadoes. We are likely to see more tornadoes today and even over the next several days.

Image courtesy of NOAA

The forecast was ultimately dependant upon two largescale steering features over the Lower 48. If the strengthening ridge over the Plains was to reach Debby, this would have taken her west into or skirting Louisiana or Texas, probably as a hurricane or the deepening trough dropping down over the Eastern US which would have taken her northeast across north Florida. While ultimately the trough will eventually steer Debby out into the Atlantic, the storm is currently in an atmospheric no mans land as neither steering flows are reaching the system and this is why the storm has stalled off NW Florida.

It looks as though the storm will creep slowly east, making a landfall Tuesday evening and should enter the Atlantioc as a depression late Wednesday if not early Thursday.

Unless the system looses all, we should see regeneration over the warm waters. Some have Debby becoming a hurricane late this week. We shall see.

Severe weather spawned by Tropical Storm Debby destroyed a home’s pool enclosure on Shore Drive in Winter Garden. (Red Huber, Orlando Sentinel / Jun 25, 2012)


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