TROPICAL CYCLONE FORMATION: T.D. KARL / T.S. LISA
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 12
MAJOR HURRICANES: 1
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good day everyone!
Tropical Storm Karl has been downgraded to a depression. As of the 11:00 a.m. advisory from the NHC, the following was available on Karl:
11:00 AM AST Wed Sep 21
Location: 20.8°N 57.8°W
Moving: WNW at 9 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 35 mph
Karl has been moving toward the WNW for the most part, however the partially exposed, somewhat ill defined center noted in satellite loop imagery, appears to have shifted to more of a westerly track over the past 4-5 hours. Based on current steering, which indicates the break in the ridge, I expect the WNW motion to continue into today, and as he approaches closer to the weakness, a turn toward the NW should occur tonight. Based on the current forecast steering layers maps, I concur with the NHC forecast track, however with the brief westerly motion noted in satellite loop imagery, I believe the track may have to be shifted west somewhat. Regardless, the center of Karl should remain east of Bermuda, albeit possibly somewhat closer.
Satellite loop imagery indicates the LLC to be slightly exposed, with the convection just to the NW edge of the center of circulation, which indicates Karl is not organized at the moment. It’s obvious (and I speak of this always), that the shear forecast indicated by various modeling, did not pan out as thought, so Karl has remained under some 15-20 knots of southerly shear, longer than anticipated, hence the weakening. The recent wind shear product may seem to indicate that the upper level anticyclone forecast to develop over Karl during the next 24 hours, may be occurring. Based on my analysis of the current shear forecast from both the GFS and ECMWF, thee upper level pattern is forecast to improve during the next 24 hours, with a supposed decrease in shear values, and the upper level anticyclone becoming established over Karl. However, based on my analysis of 500 mb humidity maps, the forecast is for a drier mid-level environment in about 48-72 hours. However, this may not be too detrimental, in that it kills the system, given the TPW values should remain high, and that the storm will be passing over warmer SST’s and OHC within the next 24 hours, through 48 hours in the forecast period. These combinations may allow for sufficient mixing out of most of the drier air. Based on these analyses, I still have to concur with the NHC intensity forecast. After day 4, Karl should come under a more baroclinic environment as the approaching trof picks him up, and the system should begin to transition into a post tropical cyclone
NHC KARL INTENSITY FORECAST
INIT 21/1500Z 20.8N 57.8W 30 KT 35 MPH
12H 22/0000Z 22.1N 59.6W 30 KT 35 MPH
24H 22/1200Z 24.0N 62.0W 30 KT 35 MPH
36H 23/0000Z 25.7N 63.6W 35 KT 40 MPH
48H 23/1200Z 27.2N 64.8W 45 KT 50 MPH
72H 24/1200Z 31.0N 62.2W 60 KT 70 MPH
96H 25/1200Z 36.0N 52.5W 70 KT 80 MPH
120H 26/1200Z 44.0N 38.5W 60 KT 70 MPH…POST-TROP/EXTRATROP
Elsewhere, Tropical Storm Lisa continues to move toward the NW over the EATL. As of the 11:00 a.m. advisory from the NHC, the following was available on Lisa:
11:00 AM AST Wed Sep 21
Location: 18.0°N 32.5°W
Moving: NW at 8 mph
Min pressure: 1002 mb / 29.59 in
Max sustained: 50 mph
Lisa has been moving NW, toward a weakness in the sub-tropical ridge in the EATL. Based on forecast steering maps, I expect this motion to continue for the next 72-96 hours, when the system will be guided around the western periphery of the ridge, due to the ridge progressing toward the east, which will impart the NNE turn.
Lisa’s cloud structure has remained pretty much the same most of today. Albeit there is an outflow channel from the western periphery of the system, and to the north and NE, Lisa is currently experiencing 20-25 kts of SW shear. This recent shear update, is once again different from the projected wind shear values and upper level pattern. However, based on the premise upper level winds could become more favorable, Lisa has a very brief window of about 24 hours, for further slow strengthening. Soon thereafter, the upper level pattern and forecast wind shear values become unfavorable for any further development of the storm. Based on this, I concur with the NHC intensity forecast, which, if shear does not decrease today, may be somewhat generous.
LISA NHC INTENSITY FORECAST
INIT 21/1500Z 18.0N 32.5W 45 KT 50 MPH
12H 22/0000Z 18.6N 33.4W 50 KT 60 MPH
24H 22/1200Z 19.7N 34.9W 45 KT 50 MPH
36H 23/0000Z 20.9N 36.5W 45 KT 50 MPH
48H 23/1200Z 22.3N 38.0W 40 KT 45 MPH
72H 24/1200Z 25.0N 41.0W 30 KT 35 MPH
96H 25/1200Z 28.5N 43.0W 25 KT 30 MPH…POST-TROP/REMNT LOW
120H 26/1200Z 34.0N 41.0W 25 KT 30 MPH…POST-TROP/REMNT LOW
Elsewhere, the GFS and ECMWF still indicate another system may roll off Africa by days 6-8 in the period. The GFS is a little more robust on the 500 mb pressure height falls than the ECMWF, and the ECMWF still indicates there may be mischief in the Bahamas as ridging builds off the SEUS coast, and height falls occur over the Bahamas area. By days 9-10, the GFS hints at development in the E. Caribbean, and indicates a 997 mb system just south of western Cuba near 83W by day 14. Granted this is 2 weeks out, the GFS has been persistent now for 3 days hinting at something in the Caribbean. The ECMWF had been more lax on this, but now looks to be trying to sniff something out in the E. Caribbean by day 9, and is a little faster with a system in the central Caribbean by day 10 and weaker.
It is suggested by both models that upper level winds could be somewhat conducive for development over that area of the Caribbean during the time mentioned. I will be monitoring this area closely, depending on whether or not subsequent model runs are consistent throughout the period
Elsewhere, Tropical Storm formation is not expected during the next 5-7 days.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS