POTENTIAL TROPICAL CYCLONE SEVEN / INVEST 99L FORECAST SYNOPSIS…ISSUED AUG. 06, 2017…5:50 P.M. EDT

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(T. F. “Storm” Walsh III)

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STORM W’s SEASONAL HURRICANE FORECAST
TOTAL STORMS: 14-16
HURRICANES:       6-8
MAJ. HURRICANES: 3-4

CURRENT TOTALS
STORMS: 5
HURRICANES: 0
MAJ. HURRICANES: 0

U.S. LANDFALLS: 2

Good evening  all!

The NHC has designated INVEST 90L, PTC SEVEN and the probability of cyclone development for the next 5 days is MEDIUM (50%) probability for INVEST 99L.

NHC 5 DAY GRAPHICAL TROPICAL WEATHER OUTLOOK (GTWO) LINKED FOR TEXT

As of 5:00 p.m. EDT, INVEST 90L has been upgraded to Potential Tropical Cyclone SEVEN.

5:00 PM EDT Sun Aug 6
Location: 15.6°N 82.0°W
Moving: WNW at 12 mph
Min pressure: 1008 mb / 29.77 in
Max sustained: 35 mph

HURREVAC NHC PTC 7 FORECAST MAPS

PTC SEVEN SATELLITE LOOP IMAGERY

WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY:

The government of Mexico has issued a Tropical Storm Warning from
Chetumal northward and around the Yucatan Peninsula to Campeche.

The government of Belize has issued a Tropical Storm Watch from
Belize City northward.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT FROM THE NHC:

A Tropical Storm Warning is in effect for…
* The coast of Mexico from Chetumal to Campeche

A Tropical Storm Watch is in effect for…
* Belize City northward to the border of Mexico

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area, in this case within 24
to 36 hours.

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, in this case within 24 to 36 hours.

Interests elsewhere around the Bay of Campeche should monitor the
progress of this system.

For storm information specific to your area, please monitor
products issued by your national meteorological service.

HAZARDS AFFECTING LAND
———————-
RAINFALL: Rainfall amounts of 3 to 6 inches, with isolated amounts
of around 12 inches, are possible across the Yucatan Peninsula of
Mexico and Belize through Wednesday. These rains could produce
life-threatening flash floods.

WIND: Tropical Storm conditions are expected to begin in portions
of the warning area by Monday afternoon or evening. Tropical Storm
conditions are possible in portions of the watch area by Monday
afternoon or evening.

Based on the most recent wind shear product from CIMSS, the disturbance is under some slight wind shear from the NW, however current motion should take it out of higher shear values tonight.  Based on analysis of forecast wind shear, the GFS, ECMWF and NAVGEM models all indicate an upper level anticyclone developing over the system, and moving in tandem with it, over the Yucatan Peninsula and BOC.  Another item causing PTC SEVEN not to be too terribly organized, is it has some slight dry air ingestion.  This is noted by the small outflow boundaries noted by the red arrows.  These are caused by thunderstorms building rapidly in the vertical, then sucking in drier air, causing the convection to collapse.  Once upper level winds become more favorable however, given the very high TPW, PTC SEVEN should be able to mix out any dry air.

LATEST WIND SHEAR FROM CIMSS

SATELLITE IMAGE SHOWING OUTFLOW BOUNDARIES

WIND SHEAR FORECAST

Based on my analysis of 850 mb winds forecast, wind shear pattern, etc., I feel we should see PTC SEVEN begin to organize and ramp up somewhat quicker once it reaches, and or passes 85W, or sooner if conditions become more favorable quicker. 

Once this system enters the BOC, an almost textbook upper level anticyclone is forecast to be over the area.  A combination of this, warm SST’s, along with the outlay of the surrounding land (the curvature south of the BOC (Yucatan/Mexico area allows to focus inflow around the storm, which is what we term forced convergence) should allow for it to spin up quickly.  Both the GFS and ECMWF are tending to indicate a potential top end CAT 1 hurricane, possible borderline CAT 2 prior to landfall.  Based on current intensity models, I cannot totally rule this out at the moment, however going with the majority, which contain 2 of the more accurate intensity models, and given the still somewhat disorganized nature of the system I am going with the lower intensity of very strong TS.  My thoughts are inline with the newly released NHC intensity forecast.

NHC INTENSITY FORECAST
INIT 06/2100Z 15.6N 82.0W 30 KT 35 MPH…POTENTIAL TROP CYCLONE
12H 07/0600Z 16.6N 83.6W 35 KT 40 MPH…TROPICAL CYCLONE
24H 07/1800Z 18.0N 85.9W 45 KT 50 MPH
36H 08/0600Z 19.0N 88.0W 45 KT 50 MPH…INLAND
48H 08/1800Z 19.9N 90.1W 35 KT 40 MPH…INLAND
72H 09/1800Z 21.0N 93.8W 60 KT 70 MPH…OVER WATER
96H 10/1800Z 21.2N 97.8W 60 KT 70 MPH…INLAND
120H 11/1800Z…DISSIPATED

The disturbance is moving WNW or (295 deg.), and I expect this motion to continue for the next 36 hours, based on forecast steering maps.  As this makes landfall over the Yucatan Peninsula, a turn more toward the west should occur, as ridging builds in north of the system, where the current slight weakness exists.  This is shown in the global models GFS and ECMWF, and as well with the dynamic guidance which is pretty much inline with the NHC forecast track

Regardless of development prior to the Yucatan Peninsula, residents in and near the path should prepare for heavy rain, flooding, and possible mudslides.  Residents of Mexico where the system could make landfall, should closely monitor this system for any significant changes, and be prepared to implement proper actions if warranted by their local NWS office.

Elsewhere, Tropical Disturbance INVEST 99L doesn’t appear as healthy as it did a few days ago.

RAMSDIS INVEST 99L SATELLITE LOOP

Analysis of water vapor imagery shows dry air IVO the system, and may be what is inhibiting development, as upper level winds are currently favorable for development, with the current shear map indicating an upper level anticyclone over the disturbance

As of the 18Z ATCF BTK product, the following was available on INVEST 99L

2:00 P.M. EDT AUG. 03, 2017
LOCATION…13.5N 41.2W
MAXIMUM SUSTAINED WINDS…30 MPH
PRESENT MOVEMENT…WNW AT 16 MPH
MINIMUM CENTRAL PRESSURE…1010 MB…29.83 INCHES

Both the GFS and ECMWF do not really indicate development down the road and keep waxing and waning the intensity, but keep it a wave/disturbance  ECMWF has been consistent on this, with the GFS pulling way back from showing a CAT2 hurricane a few days ago, to pretty much dissipating this 7-10 days down the road.  The ECMWF keeps better definition on it at about 5-6days out.  Based on current and forecast steering, the disturbance is moving to the WNW (295 deg) near 16 mph.  I expect this motion to continue until the wave reaches the Lesser Antilles area.  After that, a weakness in the ridge near the SEUS becomes apparent, and more of a northward component should occur, but remaining WNW (300-305 deg?), and is shown in the current dynamic guidance, which should be taken cautiously at the moment since the system isn’t organized.

18Z DYNAMIC GUIDANCE

One thing to bear in mind on this one…I am not inclined to drop this because it hasn’t developed yet…chances are, it may not.  However, this may be located in the Bahamas in about 5-6 days, and upper level winds are forecast to relax to favorable levels for development.  Though I’m not looking for a threat, it’s a good idea never to turn ones back on these type of systems.  I will continue to monitor this area for any significant changes.

ECMWF

Elsewhere, another strong tropical wave is exiting the African coast.  There could be a chance for some slight organization over the next 3-4 days, before westerly shear increases ahead of the wave.  I will be monitoring this for any significant changes that may occur.

RAMSDIS METEOSAT LOOP (CLICK ON IMAGE)

As a last note, DO NOT WRITE THIS SEASON OFF AS OF YET.  The following is forecast Kelvin Wave, 200mb Velocity Potential Anomalies, and MJO forecast, in that order over the next 2 weeks.

Elsewhere…I am not expecting tropical storm development during the next 5-7days.

Have a blessed day!
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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2 Responses to POTENTIAL TROPICAL CYCLONE SEVEN / INVEST 99L FORECAST SYNOPSIS…ISSUED AUG. 06, 2017…5:50 P.M. EDT

  1. Ron says:

    Thanks Storm. Quick question…is it my imagination or has the tandem of dry air and shear put the kabosh on the last few hurricane seasons. Seems like every system in at least the last couple years has really had to battle those two items just to survive. Not that that is a bad thing as it has probably saved a lot of lives and property damage. Do Pacific systems have to battle as much against dry air and shear?

    • Well, mainly dry air. Shear has been at or below climatology most of the season in the Atlantic MDR. Jul. is worse for SAL outbreaks, and sometimes into the first 10 days of Aug. A lot of the dry air as well was due to the strong sub-tropical ridge in Jul. The MJO hasn’t been on our side much this season, and is just starting to play a role over the Atlantic. During an El Nino episode, the EPAC does have to fight shear, but not necessarily drier air. The MJO hangs out mostly over the Indian Ocean, and WPAC a lot, because the sst’s are usually much warmer than ours, and they are such big bodies of water. You’ll notice at the end of my forecast, the signals upcoming are showing much better conditions, IF they are correct.

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