TROPICAL CYCLONE FORMATION: HURRICANE GASTON / T.D. 8 / T.D 9
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 7
INTENSE HURRICANES: 1
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good evening everyone!
Briefly, GASTON becomes the first MAJOR hurricane of the season. Based on forecast steering, GASTON has been drifting NW, but should begin to head toward the ENE by Tuesday, and should not pose a thereat to CONUS.
Tropical Depression 8 came to life from the area designated 91L, in between Bermuda and the U.S. east coast. Right now, the environment is not really conducive due to some 25-30 knots of southerly shear, which is exposing the LLC. The depression is moving slowly toward the WNW, and is expected to make a turn more toward the NW in 24-48 hours, and eventually recurving. Upper level winds may relax briefly, and the depression could become a Tropical Storm in the next 24 hours. This system is expected to miss hitting the coast, however if it remains a weaker system, it could move closer to the coast than projected. There are no watches out at the moment, and the following is from the NHC:
Given the uncertainty in the intensity forecast and the timing of the approach to the coast, a tropical storm watch is not being issued at this time, but one may be required later tonight.
NHC INTENSITY FORECAST
INIT 28/2100Z 31.8N 70.9W 30 KT 35 MPH
12H 29/0600Z 32.2N 72.5W 30 KT 35 MPH
24H 29/1800Z 33.0N 73.9W 35 KT 40 MPH
36H 30/0600Z 33.7N 74.9W 35 KT 40 MPH
48H 30/1800Z 34.3N 75.4W 35 KT 40 MPH
72H 31/1800Z 36.8N 72.4W 40 KT 45 MPH
I will be monitoring this during the next 3 days.
Elsewhere, INVEST 99L became better organized during the day. Based on Hurricane Hunter aircraft data, and satellite loop images, the NHC found enough evidence to designate 99L Tropical Depression NINE.
As of the 5:00 p.m. EDT advisory from the NHC, the following was available on T.D. 9:
5:00 PM EDT Sun Aug 28
Location: 23.7°N 81.7°W
Moving: W at 9 mph
Min pressure: 1009 mb
Max sustained: 35 mph
The depression is moving toward the west, and based on current and forecast steering layers maps, I expect this motion to continue during the next 24-36 hours. Depending on forward speed of the system, and timing of steering, the depression may slow it’s forward speed, with possibly a breif stall, as the ridge currently steering the depression, begins to weaken and retrograde toward the west (based on forecast steering analysis). A turn more toward the north should occur in about 3 days due to this, as the system will begin to be steered by the western periphery of the western subtropical ridge shown to be forecast centered near 23N;62W, with the combination creating a weakness along the eastern seaboard. This SHOULD lead to a NE turn shortly thereafter, with the cyclone then coming under the effect of a mid-latitude trof. I will be monitoring current and forecast steering conditions very closely over the next 3 days, and intend to update Mon.-Wed.
Based on analysis of the forecast steering, and both dynamic guidance and the global models, as well as the last ECMWF EPS tracks, the consensus right now based on everything track guidance wise, does indicate a track as shown in the NHC tracking map. The outlier was the CMC GGEM taking this north into the FL. Panhandle in 4 -5 days near Apalachicola. Given that model guidance has pretty much come into agreement of this system coming ashore over the FL. Big Bend region, I am discounting the GGEM at the moment. However, though not in the NHC discussion, I recommend residents of the Florida Peninsula from Apalachicola, to the West Central Florida area monitor the progress of this system closely, given the very wide error cone.
Tropical Depression NINE remains under very marginal conditions at the moment, as that small shear zone of 25 knots remains just north of the center. Both the GFS and ECMWF wind shear forecasts do indicated that the wind shear should diminish over the next 24 – 30 hours, still indicating the upper level anticyclone to become re-established close to, or over the center of the depression (based on current forecast track). The upper level anticyclone is forecast to fluctuate, but for the most part, should provide favorable upper level conditions after 24 hours, until time of landfall. Based on analysis of the GFS and ECMWF, both models are in agreement of either dissipating T.D. 9, or keeping a very weak system going into the Big Bend region. Given the shear forecast however, and warm Gulf waters, I am having a hard time in determining WHY, this occurs, while the 3 accurate intensity models indicate a 60 mph Tropical Storm, to a minimal CAT 1 Hurricane by day 4. The ONLY thing I can figure at the moment, is that the forecast track takes the depression over some lower OHC than what it has been experiencing. Also, analysis of the ECMWF 500 mb humidity forecast tends to indicate T.D. 9 may experience the loss of the high TPW due to the presence of dry air as it approaches the Big Bend region of Florida, although the GFS indicates a more favorable environment. The CMC GGEM still indicates a CAT 1 Hurricane in the FL. Panhandle. Given the uncertainty and discrepancies in the modeling at the moment, I have to concur with the NHC intensity forecast.
NHC INTENSITY FORECAST
INIT 28/2100Z 23.7N 81.7W 30 KT 35 MPH
12H 29/0600Z 23.9N 83.6W 30 KT 35 MPH
24H 29/1800Z 24.3N 85.4W 35 KT 40 MPH
36H 30/0600Z 24.6N 86.8W 35 KT 40 MPH
48H 30/1800Z 25.1N 87.6W 40 KT 45 MPH
72H 31/1800Z 26.8N 87.4W 45 KT 50 MPH 96H 01/1800Z 29.0N 84.5W 45 KT 50 MPH 120H 02/1800Z 31.0N 80.0W 45 KT 50 MPH
Given the wide error cone, I do recommend residents from the FL. Panhandle, to the Tampa Bay Area review any Hurricane Preparedness plans they may have. I am recommending this as a precaution at the moment, until I can see how the depression does or doesn’t develop over the next 24-36 hours, when intensity and track models should have a much better handle on the system.
At the moment, it doesn’t appear that wind will be an issue for the Florida west coast, however as this gets into the central Gulf and moves toward the north, heavy rainfall could be an issue in a few days.
The following is the current 1-3 day total rainfall forecast from the NOAA WPC:
The following NWS Warnings display map is linked…click on your area of interest for current local NWS Warnings and statements.
The following is NWS Doppler Radar loop imagery from Key West, FL.
Elsewhere, another Tropical Wave is forecast to exit the African continent either tomorrow, or early on Tues., and appears to be fairly strong and at a lower latitude as previous wave. The current wind shear forecast indicates upper level winds should be somewhat conducive for development, and the NASA GEOS model indicating moderate to high TPW associated with it. NHC currently designates a MEDIUM (50%) probability of cyclone development over the next 5 days:
I still expect an increase in activity, as the forecast calls for the MJO to be over the Atlantic Basin the next 2 weeks, and favorable 200 mb velocity potential anomalies currently entering the basin.
Have a blessed evening
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS