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(T. F. “Storm” Walsh III)
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STORM W’s SEASONAL HURRICANE FORECAST
TOTAL STORMS: 14-16
MAJ. HURRICANES: 3-4
MAJ. HURRICANES: 0
U.S. LANDFALLS: 2
Good evening all!
INVEST 99L was upgraded to Tropical depression EIGHT last night, and has just recently been upgraded to Tropical Storm GERT. INVEST 91L has been designated and is located in the far Eastern Atlantic basin. 91L has been designated a LOW (30%) probability of cyclone development over the next 5 days.
As of the 5:00 p.m. advisory from the NHC, the following information was available on GERT:
5:00 PM EDT Sun Aug 13
Location: 28.1°N 71.7°W
Moving: NNW at 10 mph
Min pressure: 1011 mb / 29.86 in
Max sustained: 40 mph
HURREVAC NHC TRACKING AND WIND MAPS
GERT is currently moving to the NNW around the western edge of the subtropical ridge. The last couple of frames in satellite loop imagery, indicates she may be making the northern turn a little earlier, as the center appears to be just east of the forecast points. In any event, I do expect the northward turn, then a turn to the NE to ENE by sometime on Tuesday. Current and forecast steering maps indicate this. Based on this analysis, I concur with the NHC forecast track, and is inline with the dynamic model guidance, as well as ensemble members. GERT should remain between the U.S. and Bermuda throughout the period.
Satellite loop imagery continues to show an organizing system.
Albeit some slight NELY shear is over the storm, there is a divergent pattern aloft, and an outflow channel is noted in the upper level wind graphic, represented by the blue colored wind flags, shown in a clockwise flow.
GERT UPPER LEVEL WIND PATTERN
Based on analysis of the forecast wind shear pattern, shear may set in briefly, however the GFS wind shear forecast does indicate the upper level anticyclone does become re-established in about 24-30 hours. Based on this, and the fact she will still be traversing 29C (84.2F) water, some further intensification should occur. Based on these factors, I agree with the NHC intensity forecast, however given the current image indicating some hot towers and over shooting tops (ARROW AND RED CIRCLES), if forecast conditions pan out, I cannot rule out GERT becoming a hurricane. I will continue to monitor this system for any significant changes.
NHC INTENSITY FORECAST
INIT 13/2100Z 28.1N 71.7W 35 KT 40 MPH
12H 14/0600Z 29.3N 72.1W 40 KT 45 MPH
24H 14/1800Z 31.1N 72.1W 50 KT 60 MPH
36H 15/0600Z 32.9N 71.3W 55 KT 65 MPH
48H 15/1800Z 35.1N 68.8W 55 KT 65 MPH
72H 16/1800Z 39.8N 59.1W 50 KT 60 MPH
96H 17/1800Z 45.0N 44.5W 45 KT 50 MPH…POST-TROP/EXTRATROP
ATCF SATELLITE CLOSEUP
Tropical Disturbance INVEST 91L has been born in the far Eastern Atlantic Basin. As of the 18Z ATCF BTK report, the following was available on INVEST 91L:
2:00 PM EDT Sun Aug 13
Location: 13.4°N 21.1°W
Moving: W at 17 mph
Min pressure: 1010 mb / 29.83 in
Max sustained: 30 mph
Satellite loop imagery indicates a fairly broad area of lower pressure over the area. Based on information contained in the 5 day Tropical Weather Outlook text, the wave, or its axis is forecast to merge with the area of low pressure.
Based on the ATCF BTK report and current satellite motion, the disturbance is moving toward the west, or even slightly south of due west, based on the fact at initialization, the “center” of the disturbance was estimated at 13.8N, and is now located at 13.4N. The 12 hour period from 06Z to 18Z today, yielded a forward speed of 17 mph. Based on current forecast steering maps, the system should continue on pretty much a west motion for the next 60-72 hours, before a WNW motion may occur, as a weakness develops in the bridging ridge (where the sub-tropical ridge has one center in the W. Atlantic, and one over the E. Atlantic and connect to each other). Although not written in stone, this may be a given, for now. Thereafter, the NHC outline in the GTWO indicates the system begins to re-curve. This will depend on how strong, or how weak the system becomes. Right now, I am not too sold on this, as in the last frame of the steering forecast loop, ridging my build north of the system. IF this becomes a hurricane as shown by the GFS, and initial guidance from the current intensity model run, a recurve would be possible, however current GFS track brings it close to the U.S. The other scenario given by the ECMWF, indicates a more westward mover, which enters the Caribbean, crosses the Greater Antilles Islands, emerges into the Atlantic jut north of the Cuban coast, and into the Florida Straits. The GEFS (ENSEMBLE SYSTEM) indicates BOTH of these solutions. The bottom line…I believe we are going to have to watch this one closely, as based on what I always preach, initial intensity and track guidance should be used just to give you the “heads up” of what “could” occur, and not be relied upon as an “official’ forecast. IF the system becomes better organized and develops, the modeling will have something more accurate to latch onto. Remember, the models are currently sampling a large, broad area…so the heat energy is strung out over a larger area at the moment.
MSLP NORMALIZED ANOMALIES FORECAST
The current wind shear analysis does show a semi-favorable upper pattern at the moment, and both the ECMWF and GFS indicate an upper level anticyclone develops over the system in about 24-36 hours and pretty much stays with the system, although there are some discrepancies as to how robust the upper feature becomes. Based on this information, should it be correct, I would not doubt if the NHC increases the probability for cyclone formation on 91L in a couple days, and I would not doubt that INVEST 91L becomes the next Tropical Depression.
I will continue to monitor this situation, however I may only have an update tomorrow, as I work Tue. – Sat this week. IF by chance this system becomes a threat to anyone by that time, I will try to make a late update in the evening after work.
IRT activity picking up, STANDBY! Everything I have been analyzing tends to indicate we could get very busy tropics wise. Of the modeling I analyzed, based on that information, we are in for a favorable Kelvin Wave pattern from around 27 Aug. through the climatological “peak” of the season, as seen in the following graphic.
KELVIN FORECAST 200 MB
You’ll also note in some of the model graphics earlier in this synopsis…models are indicating a lowering of MSLP normalized anomalies over much of the MDR and over Africa. This “lowering” of the anomalies is conducive for development.
The forecast also calls for favorable 200 mb Vertical Velocity Potential. I have compared the model graphic, against the near realtime graphic from the CPC site for yesterday. The model appears accurate. Based on these “signals” I’m seeing, indications are we should see an active remainder of the season. Remember, IRT the MJO (Madden Julian Oscillation), and the velocity potentials, increases in activity may not occur until 5-10 days past the entrance of these “signals”. The article in the following link gives a decent explanation.
200 MB VERTICAL VELOCITY POTENTIAL ANOMALIES FORECAST
On the Madden–Julian Oscillation–Atlantic Hurricane Relationship
Elsewhere…I am not expecting tropical storm development during the next 5-7days.
Have a blessed EVENING!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS