TROPICAL CYCLONE FORMATION: P. T.S. HERMINE /INVEST 92L/
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 8
MAJOR HURRICANES: 1
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good evening everyone!
Hermine has transitioned to Post Tropical Cyclone status, meaning that most of the processes keeping he going are mostly baroclinic (mostly like a mid latitude cyclone). As this process occurs, the wind field expands, and the strongest maximum winds become displaced well away from the center. As of the 2:00 p.m. EDT intermediate advisory from the NHC, the following was available on Hermine:
2:00 PM AST Sun Sep 4
Location: 37.2°N 69.3°W
Moving: ENE at 6 mph
Min pressure: 999 mb / 29.50 in
Max sustained: 70 mph
Based on my analysis of current and forecast wind shear products, and warmth of the SST’s where Hermine is located, I concur at this time with the NHC intensity forecast. Upper level winds, based on the forecast, could become briefly more favorable, leading to a reduction in wind shear, giving the possibility of Hermine re-acquiring some tropical characteristics, and could briefly transition to a sub-tropical cyclone. This is reflected in the NHC intensity forecast and forecast discussion, which in my opinion, seems reasonable, based on my analysis.
INIT 04/1500Z 37.2N 69.6W 60 KT 70 MPH
12H 05/0000Z 37.6N 69.4W 60 KT 70 MPH…POST-TROPICAL
24H 05/1200Z 38.3N 69.8W 60 KT 70 MPH…POST-TROPICAL
36H 06/0000Z 38.7N 70.0W 65 KT 75 MPH…POST-TROPICAL
48H 06/1200Z 39.0N 70.0W 65 KT 75 MPH…POST-TROPICAL
72H 07/1200Z 40.0N 68.0W 60 KT 70 MPH…POST-TROPICAL
96H 08/1200Z 41.0N 66.0W 55 KT 65 MPH…POST-TROPICAL
120H 09/1200Z 42.0N 60.5W 50 KT 60 MPH…POST-TROPICAL
Given the very large wind-field of Hermine, Tropical Storm Watches and Warnings remain in effect.
Some coastal flooding and tidal surge can still occur along the coastal areas under the watches and warnings. PLEASE follow your local NWS Statements and advisories regarding Hermine. The following link will take you to the NWS statements page, and the NWS Warning map is linked as well. Just click on your area of interest.
NWS LOCAL STATEMENTS LINK
The system continues to move slowly toward the ENE. However based on the forecast steering pattern, during the next 24-36 hours, and approaching shortwave trof, should allow for her to bend back toward the NW briefly, before steering begins to move her again to the ENE and away from the U.S. coast. This is reflected in the NHC forecast track.
The following are projected wave heights and sustained winds from the STORMSURF model:
Elsewhere, INVEST 92L has become slightly better organized. Based on my analysis of the 18Z ATCF BTK product, convection is now very close, to almost over the reported center. As of 18Z, the following information was available on INVEST 92L:
2:00 PM EDT Sun Sep 4
Location: 15.0°N 60.1°W
Moving: W at 15-20 mph
Min pressure: 1008 mb / 29.77 in
Max sustained: 35 mph
Based on that information, satellite loop imagery indicates the system has become a little better organized during the past few hours. The NHC is designating only a LOW (30%) probability of cyclone development over the next 5 days, as seen in the NHC Tropical Weather Outlook graphic.
Based on current and forecast wind shear products, this seems reasonable to me at the moment. I cannot rule out some further slow organization over the next 24 hours, however should 92L survive some of the dry air around it, I believe the best chance for further development will be once it enters the central and then, western Caribbean Sea. I am basing this upon my analysis of the forecast wind shear/200 mb streamline pattern by both the GFS and ECMWF models, which are in fairly close agreement of the upper level anticyclone becoming much better established by that time, which equates to about 78-96 hours from 12Z.
The other factors being, the OHC is extremely high in the central and western Caribbean Sea, and the PWAT forecast is calling for 92L still to retain a high value of precipitable water, which should take care of any dry air issues. We all know by now, that the shear forecast is subject to change every few days, however given the factors I just laid out, they point to conditions favorable for further (at least slow development). One hindrance is its forward speed, which may not be allowing for good surface convergence at this time. Given the above factors (should they come to fruition), I am looking for some further slow development of this system.
The system continues somewhat quickly to the west, and based on forecast steering, I expect this motion to continue during the next 96 hours, with may a slight dip just south of west briefly. Based on this, if the forecast steering pattern does not change, INVEST 92L, or whatever becomes of it, may cross the Yucatan Peninsula around Belize, or north of Belize, but still over the Yucatan Peninsula. Steering beyond that time is up in the air, but models may suggest after day 5 (120 hours), the slim probability of this entering the extreme S. GOMEX. I am not putting to much credence in this at the present time, until the system becomes better organized, so the models have a better defined LLC to initialize. Based on the 18Z dynamic guidance, I prefer the TVCN/TVCC consensus track.
I intend to have another update tomorrow sometime.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS