TROPICAL CYCLONE FORMATION: POST TROPICAL STORM 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 day everyone!
HERMINE remains a very large Post Tropical Cyclone. As of the 11:00 a.m. EDT advisory, the following was available on HERMINE from the NHC:
11:00 AM AST Mon Sep 5
Location: 38.8°N 68.8°W
Moving: NW at 6 mph
Min pressure: 998 mb
Max sustained: 70 mph
HERMINE continues to drift slowly to the NW, and this motion is expected to continue through the day. Forecast steering suggests that the surface center and mid-upper level low will rotate around each other in a counter-clockwise fashion, becoming vertically stacked in about 24-36 hours, which may bring HERMINE a little closer to the coast, before steering suggests a NNE to east motion to resume in about 48 hours.
IF this becomes vertically stacked, one would believe this wold indicate the system could intensify and try to transition briefly to a more tropical state, as the upper level pattern is forecast to become very diffluent. However, given that the cyclone is over much cooler waters of 23-25C (73-77F), these SST’s are indicative of only supporting extra-tropical to sub-tropical systems.
A Tropical Storm WARNING remains in effect, and the following are links to local NWS office statements.
NWS LOCAL STATEMENTS
The following map is linked for up to date NWS information. Click on your area, or area of interest for the latest NWS Warnings and statements.
Elsewhere, I am still monitoring INVEST 92L as it moves west in the Caribbean Sea. As of the 8:00 a.m. EDT ATCF BTK product, the following was available on INVEST 92L:
8:00 AM EDT Mon Sep 5
Location: 14.5°N 65.2°W
Moving: W at 22-25 mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 40 mph
The disturbance continues to move toward the west at a fairly robust forward speed. Based on my analysis of current and forecast steering layers maps, I expect this motion to continue through the next 72-96 hours. The latest model guidance of the consensus models tend to indicate a dive toward the WSW in about 72 hours, however a couple of the global models, and the forecast steering products tend to discount this at the moment. Based on this, I am currently calling for a continued westward motion through day 4-5. Thereafter, steering suggests the system could begin to gain some latitude, as steering appears to shift sharply to the NW for a brief period, and then weaken. At this particular point in time, it is unknown if whatever this may or may not become, enters the GOMEX past day 5. Up to that point however, I do believe this will cross over the Yucatan Peninsula somewhere near or north of Belize.
After having a brief run yesterday evening of becoming slightly better organized, INVEST 92L has seen convection wax and wane over the past few hours. Albeit the convection appears fairly consolidated, the reported center is just to the WSW of the heaviest convection. Based on my analysis of water vapor image loops, it does not appear that dry air is a problem as of yet, and the INVEST is still in an environment of high TPW.
The current problem is, it is outrunning the somewhat favorable upper level environment it had yesterday evening, and is now encountering some SWLY wind shear on the order of around 20-25 knots, as it has become positioned closer to the upper level low (ULL) to its west.
The quick forward motion (almost 5 degrees west motion in 12 hours), seems to be one of the hindering factors in lack of organization. With the lower level steering being so quick, this doesn’t allow for surface convergence to occur. However, based on my analysis of the current forecast steering, I am expecting the INVEST to slow its forward speed in about 48 hours. This may begin to help in some slow organization at that point.
Based on analysis of both the GFS and ECMWF wind shear forecast products, upper level winds appear to remain marginal during the next 36-48 hours. Shortly thereafter, both models are in fair agreement of re-establishing an upper level anticyclone over the system from about the 60-72 hour point in the forecast period. IF the INVEST can survive the current conditions, I believe we should begin to see improvement once the system reaches the central and western Caribbean Sea, as the TPW is forecast to remain high, and the system will be entering an area of some very high OHC. By all rights, should it make it through the current shear conditions, we should see some development once it reaches the area mentioned, as based on what the current model runs indicate in regard to the parameters mentioned, they point toward favorable conditions. In fact, the SHIPS, DSHP, LGEM and IVCN intensity guidance models bring the system to minimal tropical storm status by the time it reaches the Yucatan Peninsula. I cannot rule this out totally at the moment, however again, at this point and time with a disorganized system, track and intensity guidance should be deemed preliminary.
I will continue to monitor this system for any significant changes over the next 2-3 days.
Elsewhere, at the moment, I am unclear as to which tropical wave the NHC is mentioning in their 5 day graphical tropical outlook.
Satellite loop imagery indicates one wave south of the Cape Verde islands, and another right on the African coastline. The first is located approximately near 7.0N;25.0W. This wave is under marginal conditions at the moment, but is under a diffluent flow aloft, which will tend to enhance convection. The wave along the coastline, is currently under somewhat favorable conditions with a partial upper level anticyclone overhead, and a marginal upper outflow pattern. It is unclear which one of these may develop, however based on the wind shear forecast, the upper level pattern is forecast to improve during the next 72-96 hours. I will be monitoring this area as well over the next few days.
I should have another update tomorrow.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS