Tropical weather analysis - June 24, 2012

By: KoritheMan , 4:53 AM GMT on June 25, 2012

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Debby

Tropical Storm Debby remains disorganized while continuing to meander over the northeastern Gulf of Mexico. As of the latest NHC advisory, the following was posted on the storm:

Wind: 60 mph, with higher gusts
Location: 28.3°N 85.9°W
Movement: Stationary
Pressure: 991 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Satellite imagery shows the low-level center exposed, with all of the associated weather confined to a large band north and east of the center. Not surprisingly, these are also where most of the tropical storm force winds are occurring. Debby is still battling southwesterly shear being imparted by a persistent upper low over the southwest Gulf of Mexico. Size matters not. The low, while small, has ingested dry air into Debby's circulation, essentially evaporating most of the convection. While this low continues to slowly move to the southwest, it is in no hurry to do so, and the global models have been far too adamant in relinquishing the shear.



Figure 1. Latest infrared satellite image of Tropical Storm Debby. Image credit: NOAA

A slew of radar fixes from Tallahassee show little movement of the cyclone over the last several hours, although there are faint indications of a slow westward drift in recent frames. Satellite images are less inconclusive. The largely stationary motion of Debby appears to be related to rising heights over the eastern United States in the wake of the trough in this same region.

Despite the huge eastward shift in the models toward Florida today, joined by the generally reliable ECMWF, there is still a lot of uncertainty in the future trajectory, and Debby's future hangs in the balance. Water vapor, 0z upper air data from the eastern United States, as well as UW-CIMSS real-time steering data suggest that heights are gradually rising to the east of the storm as the trough lifts out. Heights above 500 mb are being a little slower to rise, and given that Debby's central pressure is still rather low, convectiveless as it is, the lingering weakness at that level may tug the storm a little northward for a little longer before weak ridging gradually builds behind the storm. However, the large scale pattern over the US and Canada favors a continuous barrage of shortwave perturbations within the mean westerly flow to periodically deamplify the ridge over the eastern US for the next several days. The result should be very little motion for the next few days, possibly stairstepping between north and west as Debby comes under the steering influence of both the ridge and the trough. The storm may finally get moving on Wednesday, when the the steering flow may finally begin to stabilize.

At that point, the ridge over the central US will reach its highest point of amplification, and if Debby moves far enough west, or lingers to the point where it avoids most of the shortwaves, it could still move westward toward the northern Gulf Coast as per earlier prognostications. On the other hand, the trough will be persistent enough just to the east of the ridge that the cyclone could find its avenue of escape through Florida, as the GFS has been showing. Either way, any appreciable movement seems likely for the next few days. Given that the Euro, albeit wildly and unpredictably, has now joined the fray in calling for a Florida landfall, I will abide by that idea for now. However, with the 0z GFS showing a blocking pattern setting up over the western Atlantic and Gulf of Mexico, westward adjustments may have to be considered tomorrow, most likely at longer-ranges. At the same time, if the GFS, now joined by the UKMET verifies, the storm will head toward peninsular Florida, and the short-term track may have to be shifted eastward. While I did mention the northern Gulf Coast, I think the large scale pattern over the US is too amplified to allow for a motion further north than the Mississippi coast.

Interests along the Gulf Coast from Louisiana to Florida should carefully monitor the progress of this tropical cyclone, which is expected to dump heavy rains. In fact, various WSR-88D radars across Florida show bands of heavy rain still training across the state. These bands have already caused flooding in some areas, as well as several tornadoes. It's also worth mentioning that the large column of dry air that has sneaked into the center over the last several hours may actually enhance the tornado potential by sunrise tomorrow, as subsidence in the middle troposphere generally leads to high dewpoint depressions, which promotes tornadic development and locally damaging wind gusts with any storms that develop along the feeder bands. Tropical storm force winds will also continue lashing much of the northeastern and eastern Gulf for the next few days, as Debby is in no hurry to go anywhere.

Debby still has the potential to intensify, though the current structure and unfavorable environment would argue against that. The global models have are clearly having issues adequately resolving the shear pattern that is affecting Debby. Thus, it pays to be conservative, and I no longer anticipate Debby becoming a hurricane. This is also supported by cold water upwelling that will inevitably impact the cyclone at some point. This is particularly true near the coast, where the shallow shelf waters have already cooled by several degrees. However, since convection is currently nonexistent over the center, presumably so is wind. Thus, no significant upwelling is forecast to affect Debby in the near-term.

Both the track and intensity forecast remain highly uncertain.

5-day intensity forecast

INITIAL 0000Z 06/25 50 KT 60 MPH
12 hour 1200Z 06/25 50 KT 60 MPH
24 hour 0000Z 06/26 50 KT 60 MPH
36 hour 1200Z 06/26 50 KT 60 MPH
48 hour 0000Z 06/27 55 KT 65 MPH
72 hour 0000Z 06/28 50 KT 60 MPH
96 hour 0000Z 06/29 45 KT 50 MPH...NEAR COAST
120 hour 0000Z 06/30 35 KT 40 MPH...INLAND

5-day track forecast



Figure 2. My 5-day forecast track for Debby.

Watches and warnings

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE MISSISSIPPI-ALABAMA BORDER EASTWARD TO THE SUWANNEE RIVER
FLORIDA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* SOUTH OF THE SUWANNEE RIVER TO ENGLEWOOD FLORIDA

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...IN THIS CASE LATER TODAY.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE
THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.

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5. Beachfoxx
5:13 AM GMT on June 25, 2012
Nice blog. Thanks!
Member Since: July 10, 2005 Posts: 157 Comments: 29383
4. MiamiHurricanes09
5:09 AM GMT on June 25, 2012
Thank you Kori. Great post per usual.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
3. traumaboyy
5:03 AM GMT on June 25, 2012
Thanks Kori!!
Member Since: August 18, 2008 Posts: 0 Comments: 2265
2. tennisgirl08
5:03 AM GMT on June 25, 2012
Nice post.
Member Since: July 17, 2008 Posts: 0 Comments: 1242
1. originalLT
5:02 AM GMT on June 25, 2012
Nice up-date, well thought out and put together.
Member Since: January 31, 2009 Posts: 0 Comments: 7443

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.