TROPICAL DISTURBANCE INVEST 96L FORECAST SYNOPSIS…ISSUED AUG. 21, 2014…8:15 P.M. EDT…WEST CENTRAL FLORIDA HURRICANE AND SEVERE WEATHER FORECAST CENTER

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Greetings everyone!

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.

NHC GRAPHICAL TROPICAL WEATHER OUTLOOK

The disturbance continues moving WNW, now at 20 mph, around the southern periphery of the subtropical ridge.

CURRENT LAYER MEAN STEERING

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.

18Z ATCF DYNAMIC GUIDANCE
96L dynamic

Analysis of satellite loop images indicates 96L is less organized as far as shower activity being located over the last reported center of circulation.

INVEST 96L FLOATER SATELLITE LOOP IMAGERY

RAMSDIS CIRA GOES EAST

CARIBBEAN SATELLITE LOOP IMAGERY

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.

VIS SATELLITE SHOWING OUTFLOW BOUNDARIES
tropical_ge_4km_visir2_floater_1_20140821184500

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. 

GFS ZONAL WIND SHEAR FORECAST


As stated, the center was found to be ill defined.  I did a close analysis of SWIR satellite loop imagery, and at 2145Z the center was located within the red circle.

SWIR SATELLITE IMAGE
swir096L-lalo

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
CoCoRAHS OBSERVER
OFFICIAL SKYWARN SPOTTER (ADVANCED)

 

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About palmharborforecastcenter

I am a Tropical Forecast meteorologist, providing hurricane forecasts during the Atlantic Hurricane Season. I retired from the U.S. Coast Guard in July of 2001. Meteorology became my passion in high school, and I have continued my educational background in meteorology since 1996, when I undertook the study of Tropical Meteorology. While working toward my degree, I had to unexpectedly withdraw from college due to my oldest sons medical reasons. I do however, meet the educational criteria of the AMS to be recognized as a meteorologist. Studies include, but are not limited to the Navy Aerographers Mate course, Naval METOC meteorology course, Meteorology 2010 Sophomore level course while attending St. Petersburg College, Clearwater, FL., Basic Forecasting course for operational meteorologists from Rapid WX, meteorology institute, a four month meteorological internship, and extensive research on numerous meteorological topics such as the MJO, NAO, satellite imagery interpretation, etc. I have been forecasting Tropical Weather (Tropical Storms and Hurricanes) since 1996, with my main client being three different Coast Guard Commands.
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18 Responses to TROPICAL DISTURBANCE INVEST 96L FORECAST SYNOPSIS…ISSUED AUG. 21, 2014…8:15 P.M. EDT…WEST CENTRAL FLORIDA HURRICANE AND SEVERE WEATHER FORECAST CENTER

  1. stefanie says:

    Thanks Storm. It’s not an easy one for sure. Glad I found you just about the time my local mets were stomping their feet and screaming on air IKE WILL NOT COME INTO THE GULF!!! LOL. Listen to him y’all. The man knows his stuff. 🙂

  2. Elliot Lisak says:

    Good Evening Senior Chief,

    I don’t want to be redundant about the praises we all give you online … however you are due the praises of those of us who rely on you and your forthright, clear and concise insight into the world of weather.

    We are still going to wait and prepare. Please remember that a Hurricane, Tropical Storm or Rain event, Wind event “it” only takes a 40 mph event, or just a lot of rain, or a lot of wind to make your life miserable.

    Therefore engage “Due Diligence” be safe think safe and act safely and we will get through .

  3. Jordan Brown says:

    The HWRF model has been very consistent showing a strong storm nearing South Florida. How serious should that model be taken given most other major models show a Northern turn?

  4. Greg goodman says:

    Thank you mr storm. I have a bad feeling about this one.

  5. Monty says:

    Thanks Storm. Damn…this is a tricky one. Am I mistaken or does guidance usually have a better grip on systems this close to the CONUS regardless if they are an Invest or Cyclone? Thank God we have you Senior Chief!!

    • No…in order for the Dynamic Guidance models to perform very accurately, there has to be a well defined LLC in place. When it’s elongated and spread out, the models cannot consolidate the vorticity and heat in one place, and in this case, with having had multiple vorticies, the models are probably going WTF?

  6. Patrick says:

    Senior, Thanks so much for the information, I’m in Texas and not wanting any bad storms but a good soaking should would help us out! Thanks again for your help better understanding!

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