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Tropical Disturbance INVEST 96L was found by Reconnaissance Aircraft a few hours ago, to have an ill defined center. As of the 18Z update of the ATCF tracking product, the following information was available on INVEST 96L:
POSITION: LATITUDE 16.4N…LONGITUDE 57.7W
MOVEMENT: WNW 20 MPH
MAX SUSTAINED WIND: 40 MPH
PRESSURE: 1009 MB/29.80 IN.
The NHC in Miami has now increased the probability for Tropical Cyclone formation of INVEST 96L to HIGH (70%) during the next 5 days.
The disturbance continues moving WNW, now at 20 mph, around the southern periphery of the subtropical ridge.
I expect this general motion to continue for the next 72 hours, with more of a POSSIBLE shift in track a little more to the west, about 280 degrees for a brief period, before coming more under the influence of the weakness in the ridge currently over the Bahamas. This weakness is what is helping to induce the northerly component in the WNW track. Based on analysis of various satellite loops, current steering strength from the PSU e-WALL site, and forecast steering layers maps, this is what I base my forecast motion on.which is verified by CIMSS vorticity maps from the 850 mb to 500 mb level. Dynamic Model track guidance was fairly inconclusive, and based on analysis, I have to go with the GFTI at the moment, but with more of a curve toward the extreme northern Bahamas.
Analysis of satellite loop images indicates 96L is less organized as far as shower activity being located over the last reported center of circulation.
CIMSS CURRENT WIND SHEAR PRODUCT
The majority of the convection is west of the circulation. I am not attributing this to wind shear, as an upper level anticyclone is clearly seen directly over the system, which was forecast by the GFS wind shear model to occur. What has happened, is albeit I thought the threat may have been less, some dry air has intruded into 96L. This was noted on earlier visible satellite imagery by the presence of outflow boundaries. Outflow boundaries occur when a system ingests dry air. This happens when thunderstorms flare up quickly, as we have seen with the increase of convection. IF dry air is close enough, the very strong updrafts feeding the thunderstorms suck in the environment that surrounds them, so when it sucks in dry air, these thunderstorms collapse, and when the quickly sinking air hits near the ocan surface, outflow boundaries occur.
Based on analysis of the current Zonal Wind shear forecast, upper level winds are still forecast to remain conducive for further development until the system gets close to or just over the eastern portion of Hispaniola. Once the system clears the Greater Antilles, upper level winds are forecast to become conducive once again.
The vorticity at 850 mb is also elongated as of my analysis.
Based on the ill defined center, we could see another reformation of the center, under the heavier convective activity to the west…however the circulation would have to slow down for this to occur.
As far as future track beyond 72 hours, I know you’d like for me to tell you EXACTLY where this is going to wind up…however if I did, I would putting out erroneous information. Given what I have analyzed, and the uncertainty as to whether or not the center could relocate, model guidance will most likely shift a couple of times before the models actually have an organized system to latch onto to provide somewhat of an accurate forecast track. At the moment, based on analysis of the current steering layers forecast maps from the PSU e-WALL site…I can only provide 2 scenarios at the moment: Forecast steering indicates 96L to continue trying to get to the weakness in the ridge. Once near the Bahamas, the steering forecast models are pretty much in agreement of the ridge center noted over the extreme GOMEX in the current steering map I posted, progresses toward the NE, and builds in over the system. Now, the thing is, one is stronger with the ridge an it’s orientation, and the other is weaker, but still has the ridge located north of the system. This leaves me with no choice but to present the following….that once this system gets to or near the Bahamas, it should begin to slow. If the ridge builds in stronger, the system COULD pose a threat toward the Florida Peninsula. If the system is too slow, and encounters weaker ridging, it COULD recurve, however it would have to be monitored closely as it would probably be a slow recurve, as Ive never seen a model try to push a system through a ridge. In any event, given the disorganized state of the system this evening, it’s just going to be a wait and see event, until the models have a better organized system to deal with, and until I can get a better LLC to work with in order to utilize near real time information for better forecast parameters. Again, if you go back to the dynamic model guidance portion of this forecast, this implores my siding with the GFTI model.
Based on all of these things I just mentioned, I am not looking for a quick ramp up in strength on this. If 96L can take care of the limited dry air by continuing to develop convection (which may become easier as the system gets over better OHC, and the shear forecast pans out) and based on the latest intensity forecast models, this could become a Tropical Depression over the next 36 hours. The intensity forecast models bring this to TS strength in about 48 hours, albeit I feel at the moment this will be slower to occur.
I will continue to monitor this system closely, and will have another update in the morning.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)