TROPICAL STORM PETER / TROPICAL DEPRESSION 17 FORECAST SYNOPSIS…ISSUED SEP. 19, 2021…1:25 P.M. EDT


Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(T. F. “Storm” Walsh)

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Please be aware, even though I do not post every night, rest assured I am continuously monitoring various areas for any significant weather.  I will be taking Sundays off (family time), unless we have active systems that may be posing a threat (i.e. Tropical, Winter Weather, Coastal Storms, etc.).
STORM WALSH PRE-SEASON FORECAST
TOTAL NAMED STORMS: 17 – 20
TOTAL HURRICANES :        7 – 9
MAJOR HURRICANES:       4 – 5

AVERAGE HURRICANE SEASON:
TOTAL NAMED STORMS: 14
TOTAL HURRICANES:         7
MAJOR HURRICANES:       3

2021 SEASON TOTALS:
TOTAL NAMED STORMS:  16
TOTAL HURRICANES:          7
MAJOR HURRICANES:        3

TOTAL U. S. LANDFALLS:    8

The following is the list of storm names for the 2021 Atlantic Hurricane Season:
Ana Bill Claudette Danny Elsa Fred Grace Henri Ida Julian Kate Larry
Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda
As a storm becomes named, I will be marking it in bold red to keep track of the activity for this Atlantic season.

Please note..when we are dealing with multiple systems, they will be listed in order as to the greatest threat to land or the U. S. , to the least threat.

Good day everyone,
The following are satellite animations of the Atlantic basin and Africa

ATLANTIC
90464608ATLANTIC
AFRICA

sat_20210919_1530_animation
INVEST 95L became a Tropical Depression last night at 11:00 p.m. EDT.  At 5:00 a.m. this morning, it was upgraded to Tropical Storm PETER.  I’m not sure what satellite imagery looked like prior to now, but the satellite presentation as of analysis indicated a rather sheared system, with the LLC being detected well west of the convection and cloud cover.
PETER IR AND VISIBLE SATELLITE ANIMATION
90464608PETER.IR
90464608PETER.VIS

 As of the 11:00 a.m. advisory, the following was available on PETER:
11:00 AM AST Sun Sep 19
Location: 17.6°N 56.5°W
Moving: WNW at 17 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 45 mph

The reported initial motion was WNW.  The NHC has mentioned that a slight shift WSW was required for initial position in a special advisory discussion, and some further southward adjustments were necessary with this advisory to come into better agreement with a blend of the GFS/ECMWF solutions that also indicate a shallower system.  I concur with this, as you can definitely see the LLC is currently on a westward motion.  Based on analysis of forecast steering layers, and analysis of the recent run of the GFS and ECMWF 500 MB geopotential height and wind speed forecast, I fairly much concur with the current track guidance consensus models and NHC track, however the exposed circulation could come a little further west before making any “turn” northward.  It is noted in the 500 mb forecast, the sub-tropical ridge remains in a weakened state, allowing for numerous “breaks” in the ridge.  One item that will play a factor in the steering of PETER, TD17, and the next wave coming off Africa, will be what is left of ODETTE, in that it is MUCH LARGER EXTRATROPICAL system.  Given the slow and erratic forecast motion of this low, it will pretty much keep a weakness in the ridging over the next 5 – 7 days.

NHC FORECAST TRACKING MAP (LINKED TO INTERACTIVE MAP)
145932_5day_cone_with_line_and_wind
ATCF GUIDANCE
aal16_2021091912_track_early
NHC SPAGHETTI PLOTS
AL16_current
ECMWF AND GFS 500 MB GEOPOTENTIAL HEIGHTS FORECAST
ecmwf-deterministic-exatl-z500_barbs-1632009600-1632009600-1632614400-40
gfs-deterministic-exatl-z500_barbs-1632031200-1632031200-1632636000-40
Maximum sustained winds were reported at 45 mph.  Since earlier this morning, PETER has begun to encounter some SW wind shear of around 20 kts, hence the exposed LLC.  The recent CIMSS shear map shows an initial position away from the shear, however the position I have circled is closer to current, which was the 24 hour forecast from 06Z (2:00 A.M.) this morning.  Analysis of the recent wind shear maps from both the ECMWF and GFS, as well as the 700 mb – 400 mb average RH forecast, indicate conditions to become more unfavorable for further strengthening during the next 24 hours.  Based on this, I do not see PETER recovering, and this could begin a weakening phase, and possibly dissipation IF the forecast conditions play out.  You can note PETER in the relation to the increased shear in the MSLP anomaly map.  For the moment, I agree with the NHC intensity forecast.
NHC INTENSITY FORECAST
INIT 19/1500Z 17.6N 56.5W 40 KT 45 MPH

12H 20/0000Z 18.3N 58.6W 40 KT 45 MPH
24H 20/1200Z 19.2N 60.8W 35 KT 40 MPH
36H 21/0000Z 20.2N 63.0W 35 KT 40 MPH
48H 21/1200Z 21.3N 64.9W 35 KT 40 MPH
60H 22/0000Z 22.5N 66.3W 35 KT 40 MPH
72H 22/1200Z 23.8N 67.0W 35 KT 40 MPH
96H 23/1200Z 25.5N 67.4W 30 KT 35 MPH
120H 24/1200Z 27.2N 66.7W 30 KT 35 MPH

PETER WIND SHEAR MAP
PETER.SHEAR

GFS WIND SHEAR FORECAST
gfs_dl_shear_carib_24
700 MB – 400 MB RH AVERAGE
gfs_rh700_400_carib_24
MSLP NORMALIZED ANOMALY MAP
gfs_mslp_sig_carib_24
I will continue to monitor Tropical Storm PETER for any changes in the forecast conditions during the next 48 hours

TROPICAL DEPRESSION 17
INVEST 97L was upgraded to Tropical Depression 17.  As of the 11:00 a.m. EDT advisory, the following was available on T. D. 17:
2:00 PM CVT Sun Sep 19
Location: 13.2°N 28.8°W
Moving: NNW at 14 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 35 mph

The depression is moving toward the NNW, and based on analysis of forecast steering, and the factors I mentioned above for PETER, I expect this motion to continue for pretty much the duration of the forecast period, however I will revisit forecast track in a couple days to see if any changes occur with the forecast ridge / trof situation.  Right now, I concur with the track guidance and NHC forecast track.
NHC FORECAST TRACKING MAP (LINKED TO INTERACTIVE MAP)
150047_5day_cone_no_line_and_wind
ATCF GUIDANCE
aal17_2021091912_track_early
NHC SPAGHETTI PLOTS
AL17_current
Maximum sustained winds were 35 mph.  Based on analysis of satellite loop imagery, the LLC was slightly exposed to the east of the heavy convection, due to some easterly shear.  However, recent satellite imagery indicated the LLC has now come almost completely under the convection.  This is most likley due to the fact of the NNW track, which is allowing the center to come under less wind shear.
T. D. 17 IR AND VISIBLE SATELLITE LOOP IMAGERY
90464608TD17IR
90464608TD17VIS
CIMSS SHEAR MAP
TD17.SHEAR
Based on this, and the forecast of a more favorable shear pattern, with a reduction in wind shear, and ample mid level moisture and SST’s of around 27C, T. D. 17 should become better organized, and I do concur with the NHC that T. D. 17 will become a Tropical Storm, in which case it will be named ROSE.  The depression has about 36 – 48 hours of forecast favorable conditions, before wind shear increases, and the system begins to be hindered by drier air in the mid level of the atmosphere.  Based on this analysis, I currently agree with the NHC intensity forecast.
NHC INTENSITY FORECAST
INIT 19/1500Z 13.2N 28.8W 30 KT 35 MPH

12H 20/0000Z 14.7N 30.1W 35 KT 40 MPH
24H 20/1200Z 16.7N 32.2W 40 KT 45 MPH
36H 21/0000Z 18.9N 33.9W 40 KT 45 MPH
48H 21/1200Z 21.0N 35.4W 35 KT 40 MPH
60H 22/0000Z 22.7N 36.5W 35 KT 40 MPH
72H 22/1200Z 24.0N 37.6W 35 KT 40 MPH
96H 23/1200Z 26.3N 39.9W 30 KT 35 MPH
120H 24/1200Z 28.3N 41.2W 30 KT 35 MPH

GFS 700 MB – 400 MB RH FORECAST AND MID LEVEL RH
gfs_rh700_400_atlantic_48
gfs-deterministic-exatl-rh500-2204000
WIND SHEAR FORECAST
ecmwf-deterministic-catl-shear_850v200-2204000
I will continue to monitor T. D. 17 for any significant changes during the next 48 hours.

Another Tropical Wave is just exiting Africa this morning.  I have chosen to wait until it clears the coast, and wait for initialization of guidance products, prior to doing any analysis and synopsis.

The following map will allow to to get information from your NWS office.
NWS WATCH / WARNING DISPLAY (LINKED…CLICK MAP, THEN YOUR AREA)

WSI DOPPLER RADAR LOOP (LINKED, CLICK RADAR MAP)

RAP RADAR (CLICK IMAGE THEN RADAR SITE…ONCE YOU CLICK THE SITE, GO TO LOOP DURATION TO CREATE A LOOP)
You may direct any questions by contacting me personally, ANYTIME, at: [email protected]

Have a blessed day!

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

 

 

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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