TROPICAL CYCLONE FORMATION: T.S. 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!
Well, add another storm to the list…what was Tropical Depression 13 in the far eastern Atlantic was recently upgraded to Tropical Storm Lisa…I will have the pertinent information further on in the synopsis.
Tropical Storm Karl continues to be plagued by southerly wind shear, which has exposed the LLC. As of the 11:00 a.m. advisory from the NHC, the following was available on Karl:
11:00 AM AST Tue Sep 20
Location: 20.0°N 54.3°W
Moving: W at 17 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 40 mph
Karl has been under southerly to SSW wind shear over the past few hours, with the last CIMSS wind shear product indicating only 15 knots of shear. This has caused the LLC to be slightly displaced to the SW of the heavy convection. Based on my analysis of the current wind shear forecast from both the GFS and ECMWF models, wind shear should begin to relax after the next 24 hours, with the premise of an improving upper level 200 mb pattern.
In any case, wind shear is forecast to relax after 24 hours, and analysis reveals mid level humidity is forecast to increase, and the cyclone will be moving over higher SST’s and slightly higher OHC. This should allow Karl to begin some slow strengthening. About 48 hours into the forecast period, shear is forecast to be pretty low, and an upper level anticyclone which is forecast to develop over Karl, becomes pretty well established, with the 200 mb streamline pattern indicating pretty favorable conditions…This should allow Karl to attain category 1 hurricane status either by that time, or shortly thereafter. Given the forecast of increased moisture, and the upper level pattern, Karl should intensify at a more steady rate from 72 hours on. Analysis of forecast wind shear values however, suggest that after 96 -120 hours, wind shear values increase, which should put a damper on further strengthening. The NHC intensity forecast seems reasonable at the moment given the mentioned forecast parameters, and I concur at this time. Depending on how actual conditions materialize, Karl could posses the potential to become a minimal CAT 3 hurricane by day 5, if conditions pan out.
Karl has been moving to the west most of the morning, and I expect this motion to continue through today, and possibly for the next 36 – 48 hours. Thereafter, the storm should be close enough to feeling the weakness in the subtropical ridge, and begin to turn toward the WNW then NW. By 72 hours, a 500 mb trof digging southward should begin to pick up Karl, and turn him toward the NE. Analysis of forecast steering maps, and 500 mb maps of the GFS and ECMWF are in agreement of this, and the NHC track is indicative of the dynamic model consensus, which was clustered tighter at 18Z. However I must say, with the continued westward movement as of this synopsis, should it continue, I feel the track could be shifted left, which would put Bermuda at more of a risk for the center of the system to pass closer. Hopefully, that won’t be the case, and for right now, the forecast calls for Karl to pass east of the island. Residents of Bermuda should monitor the progress of Karl closely, for any significant changes.
Elsewhere, Tropical Depression 13 was upgraded to Tropical Storm Lisa a short time ago. The following information was available on Lisa as of the 11:00 a.m. advisory from the NHC:
11:00 AM AST Tue Sep 20
Location: 15.3°N 30.4°W
Moving: NW at 12 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 40 mph
Current satellite loop imagery indicates Lisa is becoming a little better organized, with a flare up of convection near the center, and she may be trying to develop a CDO. Based on analysis of the current CIMSS wind shear an upper level satellite derived winds products, Lisa is under favorable conditions for further slow strengthening. Albeit some limiting factors exist, such as the large circulation and marginal mid level moisture. Based on my analysis of the current wind shear forecast, and forecast shear values, Lisa has about a 48 hour window for further strengthening, before upper level winds and 200 mb pattern become non conducive for further development. Given the above, I concur at the moment with the NHC intensity forecast. Based on the satellite loop imagery however, showing an improving structure, I feel that strengthening may be a little quicker these next few hours, and she could possibly reach 45 mph by next advisory.
NHC INTENSITY FORECAST
INIT 20/1500Z 15.3N 30.4W 35 KT 40 MPH
12H 21/0000Z 16.2N 31.5W 35 KT 40 MPH
24H 21/1200Z 17.3N 33.2W 40 KT 45 MPH
36H 22/0000Z 18.2N 35.0W 45 KT 50 MPH
48H 22/1200Z 19.1N 36.4W 50 KT 60 MPH
72H 23/1200Z 21.7N 39.0W 40 KT 45 MPH
96H 24/1200Z 24.5N 41.4W 30 KT 35 MPH
120H 25/1200Z 28.3N 43.6W 25 KT 30 MPH…POST-TROP/REMNT LOW
Lisa is currently heading to the NW, and I expect this motion to continue as a break in the ridge NNW of the system persists. This motion should continue for the next 4 days, until the storm reaches the extent of the western periphery of the ridge. At that time, the storm should begin a turn north, then NE as it moves around the western portion of the ridge. This has been pretty much the scenario form the get go, and analysis of forecast steering layers maps doesn’t indicate any change. Based on this, I concur with the NHC forecast track.
Elsewhere, analysis of the GFS and ECMWF are in fir agreement of the pattern I spoke of Saturday,. In the 6-10 day period, albeit there is a slight difference in timing, both the GFS and ECMWF initiated another low to be off the African Coast near the Cabo Verde Islands by around day 7-8 in the forecast period. In addition, in the 7-10, indications are still present of a ridge moving off the SEUS, with the premise of lowering 500 mb pressure heights anywhere from the Bahamas, into the E. GOMEX. This scenario has to be watched, as it’s close to that time in the season when we begin to focus on the Caribbean and GOMEX / Bahamas area. This setup is generally indicative of the possibility for another close in development (i.e. Ian;Hermine). In addition, the GFS is much more bullish, but has been consistent for 2 runs today, and the ECMWF hinting at a weak lowering of pressures, in the eastern Caribbean by day 10. Given the pattern which is forecast, I cannot rule out something in the Caribbean at the moment, during that particular time frame, although I am more interested in the Bahamas area during that time. I will be monitoring the area closer as we get closer to that time in the forecast period, especially if models continue to show continuity.
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