TROPICAL DISTURBANCE INVEST 99L FORECAST SYNOPSIS…ISSUED AUG. 20, 2016…7:50 P.M. EDT

TROPICAL CYCLONE FORMATION: T.S. FIONA / INVEST 99L (60%)/ EATL DIST (70%)

Disclaimer:  This site is not affiliated with the National Hurricane Center, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.
(T. F. “Storm” Walsh III)

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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:

TOTAL STORMS: 6
HURRICANES: 2
INTENSE HURRICANES: 0
U.S.LANDFALLS: 2

StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
HURRICANES: 6-7
INTENSE HURRICANES: 3-4

Good evening  everyone!

This evenings forecast will focus on Tropical Disturbance INVEST 99L, as Tropical Storm Fiona continues to move to the NW, and this track is forecast to continue during the next 4-5 days, along with her forecast to weaken to a remnant low.  One thing about Fiona however is, the remnant may not re-curve right away, as in 4 days, steering currents become weak, and forecast steering shows the remnant may begin to head back to the west for a brief period.  The EATL Disturbance has just exited the African coast, and forecast steering indicates this should perform almost an immediate re-curve.

NHC 5 DAY GRAPHICAL TROPICAL WEATHER OUTLOOK
two_atl_5d0

Satellite loop images indicate INVEST 99L is not very well organized at the moment.  Earlier this afternoon, 99L appeared to have had convection coalesce symmetrically.  However, since then, the reported center is located to the north of the heavy convective area.  Based on the 18Z ATCF BTK product, the following was available on INVEST 99L:

2:00 PM AST Sat Aug 20
Location: 12.0°N 38.0°W
Moving: W at 17 mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 30 mph

INVEST 99L SATELLITE LOOP IMAGERY
avn0-lalo99L

RAMSDIS FLOATER SATELLITE LOOP 99L
tropical_ge_4km_ir4_floater_2

Upon analysis of water vapor loop imagery, and MIMIC TPW animation, 99L appears to have taken in some drier air.  However, you’ll note in the MIMIC TPW loop, it appears that 99L “”ate” the dry air.  The drier air appears north of the TPW associated with 99L as a blue blip…a few frames later, you can see 99L eat the blip.

99L WATER VAPOR LOOP
wv0-lalo99L

MIMIC TPW LOOP
latest72hrs

Analysis of the 850 mb vorticity product does agree with the reported center location.  Based on satellite loop imagery, lower convergence, and upper divergence products, It would not surprise me to see a possible center reformation try to occur under the heavy convection. 

CIMSS 850 MB VORTICITY
wg8vor

LOWER CONVERGENCE
wg8conv

UPPER DIVERGENCE
wg8dvg

99L has been under some slight shear during the past few hours, as the orientation of the upper level anticyclone had been such that the upper level flow has not been optimal.  The recent shear product shows the center of the upper level anticyclone has inched closer to the reported center, while the heavy convection is under 20 knots of easterly shear.  This may continue for the next 24 hours, possibly 36.  However, 42 hours into the forecast period from 12Z, information from the NOAA RUC HFIP site shows both the GFS and ECMWF in agreement of wind shear falling to 10 knots and below.  Analysis of the GFS wind shear forecast map indicates the upper level anticyclone may be close to, or centered over the disturbance by that time.  Given this premise, and seeing how 99L has a lot of high TPW content, I believe INVEST 99L should start to become better organized, and begin  slowly develop.  Another factor in this slow process is, this system has a very large circulation, so it is going to take some time for it to consolidate.  IF the center does in fact reform under the convection, development could begin to occur sooner.  If not, then I feel the current intensity guidance may be a bit quick in bring this to T.S. status.  I would mention however, the 3 models most widely used in intensity guidance (SHIPS, DSHP, and LGEM) have been consistent in bring this system to CAT 2 Hurricane status in 5 days.  This may be overdone, as 99L is still lacking a closed LLC.  This means the models do not have a closed, warm core center to initialize.  Based on  this, dynamic model track guidance and intensity guidance should be considered PRELIMINARY, and considered only an approximation.   However, should 99L mix out the drier air, the GFS wind shear forecast not only calls for the upper level anticyclone to develop over the system, the upper feature becomes pretty textbook, and moves in tandem with 99L.  Base on this premise, a hurricane within 5-7 days cannot be ruled out at the moment.

99L WIND SHEAR PRODUCT
tccaptureshear99L

99L TPW
tccapturetpw99L

18Z ATCF INTENSITY GUIDANCE
99L 18Z INTENSITY GUIDANCE

INVEST 99L continues to move toward the west, and I expect this motion to continue during the next 48-60 hours, before beginning to move more toward the WNW.  This motion will be in response to a break in the subtropical ridge near approximately 28-30 N;62W.  At the moment, based on analysis of the forecast steering layers maps, valid for 00Z this evening, the flow on the southern periphery of the ridge may be strong enough as to not allow the break to pull 99L north.  The forecast weakness in the ridge appears to be weak enough to only impart a WNW motion on 99L.  This is currently supported by the GFS Ensemble members, and dynamic model guidance based on the 18Z ATCF update.  The two more accurate models TVCN/TVCA continue to bring 99L into the Caribbean, and then over Hispaniola.  Some of the other modeling is slightly to the right.  I currently prefer the TVCA/TVCN consensus.  Should this motion occur, after that, steering will be tricky…as the steering layers forecast models only go out 6 days.  The possibility at the moment suggests that the FL. Peninsula may be threatened, while another probability is the U.S. east coast could be threatened.  My thoughts on this are based on what the steering forecast maps indicate.  It is the unknown variable of whether or not the western ridge forecast for over the Gulf coast states in 5 days extends eastward enough to help steer 99L more toward the west, or whether or not the flow around the very edge weakness allows it to move further northward, closer to the eastern Seaboard.  Again, model guidance is still preliminary, however the general consensus is that a possibility for 99L to become a U.S threat exists at the moment.

18Z ATCF DYNAMIC GUIDANCE
99L 18Z DYNAMIC GUIDANCE
GEFS GUIDANCE (ENSEMBLE) 12Z
gefs_AL99_2016082012

ECMWF ENSEMBLE GUIDANCE (YESTERDAY EVENING)
eps_AL99_2016082000

EARLY MODEL CONSENSUS 18Z
99L 18Z EARLY CONSENSUS
This is not to alarm anyone, however it is my recommendation that residents of the FL. Peninsula, and along the eastern Seaboard monitor this system closely.  Although these  uncertainties, this would be an excellent time to review hurricane preparedness plans in these areas.

I intend to have another update tomorrow late afternoon or early evening.

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
CoCoRAHS OBSERVER

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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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5 Responses to TROPICAL DISTURBANCE INVEST 99L FORECAST SYNOPSIS…ISSUED AUG. 20, 2016…7:50 P.M. EDT

  1. Teresa criat says:

    Thanks a bunch, once again, for your excellent interpretation of all that data!!! Wow! Keep us posted when you can!

  2. Monty says:

    Thanks Storm. Guess we need to keep an eye on 99L..at least for now.

  3. E.M. Lisak says:

    Excellent synopsis, like usual, no hype just real time info. We have all gone through the drill. Every year since Andrew I have been prepared. I did the last preparation today took down my huge Mangoe tree …. it was threatening my home and my neighbors. I might finally have the opportunity to use all my D batteries. Next to pre-prep all my clients homes. NRN (No response required). Be safe everyone.

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