TROPICAL STORM IAN / TROPICAL WEATHER FORECAST SYNOPSIS…ISSUED SEP. 12, 2016…12:25 P.M. EDT

TROPICAL CYCLONE FORMATION: T.S. IAN

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(T. F. “Storm” Walsh III)

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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:

TOTAL STORMS: 9
HURRICANES: 4
MAJOR HURRICANES: 1
U.S.LANDFALLS: 3

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

Good day everyone!

Cloudiness and showers continue to persist over the northern Bahamas this morning associated with the remnants of ex-INVEST 93L.  Analysis of the current vorticity product from CIMSS indicates this area displays good vorticity at the 850-700 mb level.  Vorticity is present at 500 mb, however not as strong, and to the SE of the 850-700 mb vorticity.  Mid level circulation is noted, however the area is currently under about 25 kts of NWLY wind shear, keeping convection to the SE of the main circulation.  This is why the vorticity product indicates what it does, showing that this area is tilted to the SE.

RAMSDIS FLOATER SATELLITE LOOP
tropical_ge_4km_ir4_floater_2

tropical_ge_4km_visir2_floater_2

This area of disturbed weather is moving to the WNW, and should cross into the Florida peninsula within about the next 24-36 hours.  While I do not expect development of this as it moves WNW, steering suggests this may exit the Florida peninsula over the extreme NE GOMEX by 72 hours.  There may not be enough time over water from that point, and close proximity to land combined with this, may inhibit organization in the NE GOMEX.  I will monitor this however, as the GFS indicates wind shear to drop briefly to near zero over the area by then, with shear only picking up to 10 knots.  Regardless, this weather should menace precipitation probabilities over Florida within the next 2 days as it moves WNW across the state.

GFS WIND SHEAR FORECAST
gfs_dl_shear_watl_11
Elsewhere, Tropical Disturbance INVEST 94L has been upgraded to Tropical Storm IAN.  Recent satellite loop imagery indicates the low level circulation has become better defined this morning.  I have only one problem with this…the naming of this with it looking like it does in the current state, I have to SMH, as the low level circulation is exposed from the convection, approximately 70-80 miles SW.  Based on the criteria from the NHC, organized thunderstorm activity needs to persists over or close to the center of the LLC for at least 12-24 hours.  They seem to do this EVERY season.  I remember last season they named a naked swirl.  SMH.  In any event, the following was available on IAN from the NHC 11:00 a.m. EDT advisory:

11:00 AM AST Mon Sep 12
Location: 21.8°N 50.4°W
Moving: NW at 13 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 40 mph

HURREVAC NHC TRACKING MAP
hurrevac-ian-error

IAN FLOATER SATELLITE LOOP
avn0-lalo-ian

rgb0-lalo-ian

Based on analysis of the current wind shear product from CIMSS, the center of the disturbance was located just to the north of an upper level anticyclone.  Given the orientation of the system, the upper level setup is currently producing 30-35 knots of SW shear, which is impinging on the western periphery of the disturbance.

CIMSS WIND SHEAR FOR TS IAN
tccaptureshear-ian

The current wind shear forecast from the GFS indicates the upper level environment should improve over the next 36-48 hours, with shear relaxing somewhat, and the upper level anticyclone becoming established more over the center of circulation.  This should allow for the LLC to come under the heavy convection.   Based on this analysis from this morning, I concur at the moment with the NHC intensity forecast, however I’m sure adjustments will be made as we see how the shear actually plays out.

NHC INTENSITY FORECAST

INIT 12/1500Z 21.8N 50.4W 35 KT 40 MPH
12H 13/0000Z 23.4N 51.2W 35 KT 40 MPH
24H 13/1200Z 25.4N 52.4W 35 KT 40 MPH
36H 14/0000Z 27.3N 53.6W 40 KT 45 MPH
48H 14/1200Z 29.7N 54.8W 45 KT 50 MPH
72H 15/1200Z 34.5N 53.8W 50 KT 60 MPH
96H 16/1200Z 42.5N 45.5W 50 KT 60 MPH
120H 17/1200Z 53.0N 32.0W 50 KT 60 MPH…POST-TROP/EXTRATROP

IAN is moving to the NW, and I expect this motion to continue for the next 48-60 hours, as he moves through a break in the sub-tropical ridge, which is shown in the current steering layers forecast maps.  After that, I expect a turn more toward the north, then NE as a trof approaches the storm, and eventually re-curves it.

I will continue to follow this system, until re-curvature takes place.

Elsewhere, another Tropical Wave appears to be somewhat slightly organized this morning, and is located just off the African coast.  Upper level winds are currently marginal for further slow development, however the wind shear forecast indicates upper level winds to become more conducive over the area in about 48 hours or so.  This may allow for this disturbed weather to become gradually better organized.  Satellite loop imagery at the moment shows a more westward movement.  However, I do believe a motion toward the WNW may ensue, as this wave should experience influence from a break in the ridge, just to its NW.  Based on forecast steering, this may very well be sacrificed into the re-curvature zone.  It’s near that time of the season, where re-curvature off Africa may begin to be the norm.  There are possibilities however, this time of the season, if one sneaks low enough (below 10N), to maybe come further west.  However, we will soon be coming up  on climatology, where we begin to once again focus on the Caribbean Sea and GOMEX for development.

RAMSDIS METEOSAT LOOP IMAGERY
tropical_met_4km_ir4_floater

tropical_met_4km_visir2_floater

Speaking of which, based on my analysis of the GFS and ECMWF 500 mb normalized anomaly maps this morning, a strong ridge of high pressure is forecast to build north of the New England area over Canada, with secondary ridging off the U.S. east coast, in about 8-10 days.  In turn, lowering pressure heights can be noted in the Caribbean Sea…meaning the area may have to be monitored for any situational development.

GFS / ECMWF 500 MB NORMALIZED ANOMALIES FORECAST
gfs_z500_norm_atlantic_39
gfs_z500_sig_mex_39

ecm_z500_anom_conus_9

ecmwf_z500_norm_noram_34

I should have another update tomorrow.

Elsewhere, Tropical Storm formation is not expected during the next 5-7 days.

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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