TROPICAL DEPRESSION PETER / TROPICAL STORM ROSE / INVEST 98L FORECAST SYNOPSIS…ISSUED SEP. 21, 2021…9:10 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:  17
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 evening everyone,
The following are satellite animations of the Atlantic basin and Africa
ATLANTIC
92736735ATL
AFRICA
sat_20210921_2215_animation

TROPICAL DEPRESSION PETER
PETER has been downgraded to a Tropical Depression.  As of the 5:00 p.m. advisory, the following was available on Peter:
5:00 PM AST Tue Sep 21

Location: 20.5°N 65.0°W
Moving: WNW at 8 mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 35 mph
According to the NHC, PETER is heading to the WNW.  Satellite imagery animations indciate the LLC may be still moving a tad more west, but is beginning to follow the convective pattern.  Based on this, and analysis of forecast steering layers, I agree with the NHC track, however only after I can clearly see lack of a more westward component.  Model guidance indicates pretty much the same track, however after 48 hours, shows a large spread.  Regardless, PETER should head for a weakness in the ridge through the forecast period.
NHC FORECAST TRACK
205016_5day_cone_no_line_and_wind
ATCF 18Z GUIDANCE
aal16_2021092118_track_early
NHC SPAGHETTI PLOTS
AL16_current
Satellite loop imagery still indicates PETER is under wind shear
PETER SATELLITE ANIMATIONS
PETER.IR
PETER.VIS
CIMSS WIND SHEAR MAP AND UPPER LEVEL WINDS
PETER.SHEAR
PETER.UPPER
Based on analysis of forecast humidity values, and wind shear, shear is supposed to remain and increase during the remainder of the forecast period, with mid level dry air eventually becoming entrained.  In fact, both the ECMWF and GFS indicate the seam fate for Tropical Storm ROSE.  Based on analysis of this data, I believe PETER should become a remnant in a couple of days, and I agree at the moment with the NHC intensity forecast.
NHC INTENSITY FORECAST

INIT 21/2100Z 20.5N 65.0W 30 KT 35 MPH
12H 22/0600Z 21.3N 66.1W 30 KT 35 MPH
24H 22/1800Z 22.3N 67.2W 25 KT 30 MPH
36H 23/0600Z 23.2N 67.4W 25 KT 30 MPH…POST-TROP/REMNT LOW
48H 23/1800Z 24.2N 66.9W 25 KT 30 MPH…POST-TROP/REMNT LOW
60H 24/0600Z 25.3N 66.1W 25 KT 30 MPH…POST-TROP/REMNT LOW
72H 24/1800Z 26.7N 65.1W 25 KT 30 MPH…POST-TROP/REMNT LOW
96H 25/1800Z 28.7N 63.7W 25 KT 30 MPH…POST-TROP/REMNT LOW
120H 26/1800Z…DISSIPATED

TROPICAL STORM ROSE
ROSE is barley hanging on to Tropical Storm status.  As of the 5:00 p.m. advisory, the following was available on ROSE:
5:00 PM AST Tue Sep 21
Location: 22.5°N 37.7°W
Moving: NW at 10 mph
Min pressure: 1008 mb / 29.77 in
Max sustained: 40 mph
ROSE is currently moving to the NW.  Based on analysis of forecast steering layers, and current model guidance, this motion should continue for the next 36 hours, before a slowing in forward speed occurs, along with a northward turn, followed by a NE motion.  Again, this will be due to a weakness in the sub-tropical ridge.  Based on this, I concur with the NHC forecast track.
NHC FORECAST TRACK
203736_5day_cone_no_line_and_wind
ATCF 18Z GUIDANCE AND NHC SPAGHETTI PLOTS
aal17_2021092118_track_early
AL17_current
Based again on analysis of the 500 RH forecast and wind shear forecast, wind shear is forecast to increase over ROSE, and dry air intrusion seems evident in the mid levels later in the period.  The following CIMSS map indicated shear over ROSE at time of analysis,and the upper level pattern did not indciate outflow.  Satellite imagery indicated and exposed LLC west of the convection.
CIMSS WIND SHEAR AND UPPER LEVEL WINDS
ROSE.SHEAR
ROSE.UPPER
ROSE SATELLITE ANIMATION
ROSE.IR
Based on the current forecast conditions, I expect ROSE to weaken, although shear reduces for a brief period, and convection may try to rebuild near the center, which could result in some brief, slight intensification, however the general trend does indciate weakening.  Based on this, I agree with the NHC intensity forecast.
NHC INTENSITY FORECAST

INIT 21/2100Z 22.5N 37.7W 35 KT 40 MPH
12H 22/0600Z 23.5N 38.6W 30 KT 35 MPH
24H 22/1800Z 24.8N 39.8W 30 KT 35 MPH
36H 23/0600Z 26.2N 40.8W 30 KT 35 MPH
48H 23/1800Z 27.5N 41.3W 30 KT 35 MPH
60H 24/0600Z 28.8N 40.7W 30 KT 35 MPH
72H 24/1800Z 29.8N 38.8W 30 KT 35 MPH…POST-TROP/REMNT LOW
96H 25/1800Z 31.5N 33.5W 25 KT 30 MPH…POST-TROP/REMNT LOW
120H 26/1800Z…DISSIPATED

INVEST 98L
INVEST 98L has seemed to change little as far as structure, however it appears to be getting slowly better organized.  In fact, the last few frames in the animation show a slightly better system than a couple of hours ago.  98L is under a low shear environment, albeit it still lacks any notable outflow in the upper atmosphere, the shear map may indicate outflow may be slowly trying to take shape.
98L SATELLITE ANIMATION
INVEST.98L
The system was moving toward the west at around 14 mph, and maximum winds were 30 mph.
Based on analysis of forecast steering layers, I expect this motion to continue for the next couple of days, although the last  updated guidance at time of analysis indicated a more WNW motion in 48 hours.  However, the ECMWF indicated a more westward motion in the forecast period out to 120 hours, which was further west than the GFS earlier run.  However, the latest GFS run has shifted more toward the west in a similar fashion as the ECMWF, but tends to move the system more to the WNW, and eventually northward.  Now, this is all going to depend on how strong 98L (forecast to be SAM) becomes.  The weaker the system, the more it will have a tendency to retain a more westward component.  The stronger the system, the more of a northward component will be likely.  Right now, based on what I saw in forecast steering analysis, I believe 98L will move a bit further west before making a WNW turn.  In the graphics, I did not go beyond 5 days in the forecast period, as we know how accuracy becomes less reliable after that.  It is noted in the 500 mb height forecast, that riding does remain around 98L.  Right now, it is unknown if this system will definitely affect the U. S. in anyway, but it may be a good idea to keep close tabs on it.
ATCF 18Z GUIDANCE AND NHC SPAGHETTI PLOTS
aal98_2021092118_track_early
AL98_current
CIMSS WIND SHEAR AND UPPER LEVEL WINDS
98L.SHEAR
98L.UPPER
Based on analysis of forecast wind shear from both the ECMWF and GFS, the pattern is forecast to become more favorable during the next 5 days, and by days 4 and 5, and almost complete radial outflow pattern is forecast in the upper levels.  In fact, the 18Z SHIPS diagnostic report indicates wind shear is forecast to reduce, and remain below 15 kts during the next 5 days, with shear values dropping into the single digits in about 12 hours, through 96 hours in the forecast period.  Both models show a very favorable 500 mb RH conditions at day 5 as well.  IF these conditions materialize, I believe 98L should become a Tropical Depression  within the next 24 hours, and Tropical Storm SAM by 48 hours.  Analysis of the MSLP anomalies forecast indicates a track further west, and both models indicate SAM to become a hurricane by day 7.  However this should be considered low confidence at this time, until we see how forecast conditions pan out.
ECMWF AND GFS MSLP ANOMALY FORECAST
ecmwf-deterministic-catl-mslp_norm_anom-2657600
gfs_mslp_sig_westmdr_120
WIND SHEAR FORECAST
ecmwf-deterministic-catl-shear_850v200-2657600
gfs_dl_shear_westmdr_120
200 MB FORECAST PATTERN
ecmwf-deterministic-catl-z200_speed-2657600
gfs_uv250_westmdr_120
MID LEVEL RELATIVE HUMIDITY FORECAST
ecmwf-deterministic-catl-rh500-2657600
gfs_rh700_400_westmdr_120
I will be monitoring the progress of 98L closely during the next 72 – 96 hours

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 evening!

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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