TROPICAL STORM GRACE AND HENRI FORECAST TO BECOME HURRICANES…ISSUED AUG. 17, 2021…9:30 P.M. EDT

TROPICAL STORM GRACE AND HENRI FORECAST TO BECOME HURRICANES…ISSUED AUG. 17, 2021…9:30 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:  8
TOTAL HURRICANES:        1
MAJOR HURRICANES:      0

TOTAL U. S. LANDFALLS:  4

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,

I did not issue a forecast last night, as when I got home from work, I had to do some car repairs.  This evening I’m going to start with the Africa satellite image.  As you can see, waves appear to be getting stronger.  There is currently one wave that has just exited the African coast.
AFRICA SATELLITE ANIMATION
Cayman Islands
TROPICAL STORM GRACE
GRACE has once again become a Tropical Storm.  Recent satellite loop imagery indicates GRACE is becoming better organized.  You can clearly pick out the center of circulation in the visible animation.  The center is just west of Jamaica, and is just west of the heaviest convection.  This is most likely due to some wind shear GRACE was under earlier.  I analyzed water vapor imagery, and it appears GRACE is barely fighting off dry air, however she seems to be staving it off.
GRACE IR AND VISIBLE SATELLITE ANIMATIONS FROM WEATHERNERDS
Cuba
ECMWF ENSEMBLE
As of the 8:00 p.m. EDT intermediate advisory from the NHC, the following was available on GRACE:
8:00 PM EDT Tue Aug 17
Location: 18.3°N 78.6°W
Moving: W at 15 mph
Min pressure: 1002 mb / 29.59 in
Max sustained: 60 mph

Based on satellite motion, and current steering layer mean, GRACE is moving to the west, to just north of west.
CURRENT STEERING LAYER MEAN FROM CIMSS
Haiti
Based on my analysis of forecast steering (unfortunately, I have only one steering forecast map available which is the GFS as the PSU E-wall site forecast steering maps page has not been available, which contained maps from the GFS, CMC, and NOGAPS), and analysis of the GFS and ECMWF 500 mb height and wind speed maps, GRACE should continue on this track through this evening, with a possible WNW motion with a more westerly component.  Based on this, GRACE should pretty much follow the model guidance and NHC forecast track.  I do believe the possibility may exist, since GRACE is forecast to become a hurricane and will be steered by the 850 – 400 mb layer, she could feel the weakness in the western periphery of the ridge, and could shift slightly more to the WNW, following the most northern ECMWF ENSEMBLE members.  Right now, even based on that, I do not feel at this time that Texas will take a direct hit.
NHC TRACKING MAP
INLAND
TRACKING MAP LINKED TO INTERACTIVE TRACKING MAP
INLAND

ATCF 00Z GUIDANCE AND 12Z ECMWF EPS
Peninsula of Mexico
Punta Herrero
Maximum sustained winds associated with GRACE were reported to be 60 mph.  Grace has moved into an area where wind shear has become light, and an outflow pattern appears to in place and probably developing, suggestive of weak shear.
GRACE WIND SHEAR FROM CIMSS
Rhode Island
GRACE UPPER LEVEL WINDS
satellite image
Based on analysis of forecast wind shear, and 200 mb streamline maps, albeit not the most optimal, the models show an improving upper level pattern, with the forecast wind shear pattern showing the same anti-cyclonic flow over the center of GRACE up until she reaches the Yucatan Peninsula.  200 mb streamlines indicate light 200 mb winds, with a unidirectional flow, vice a strong radial outflow.  Once she enters the BOC however, this pattern becomes briefly disrupted, but recovers at 72 hours in the forecast period with anti-cyclonic flow from the eastern periphery, around to the west to NW.  SHIPS diagnostics indicated the mid level humidity values to be marginal, analysis of both the GFS and ECMWF humidity forecast indicates a more favorable moisture filed.  Based on these criteria, I agree that GRACE should reach hurricane status sometime tomorrow.  IF the global models are correct, especially with the wind shear pattern (which we saw in the forecast with FRED, in which the anti-cyclonic flow was centered over him), GRACE should continue to strengthen up until she encounters the Yucatan Peninsula.  However, even if humidity values do become marginal, she will be crossing over some very high OHC.  This could compensate for moisture values.  Based on the OHC values, IF things come to fruition as per the global models, I cannot rule out a possibility of Rapid Intensification as she traverses the Caribbean.  Values of 50+ will sustain a major hurricane, and allow for R. I.  Should R. I. not occur, I feel she may intensify at a more steady rate than shown in the NHC intensity froecast.  You’ll note in the shear forecast, the red “L”, which is the symbol for low pressure, and indicating the center of the storm.
GFS 12, 30, 54, AND 72 HOUR SHEAR FORECAST MAPS
satellite motion
Southern coast
southern Cuba
OCEAN HEAT CONTENT
Texas
At this time, I agree with the NHC intensity forecast, however do not be surprised if the forecast intensity values increase sometime tomorrow.
NHC INTENSITY FORECAST
INIT 17/2100Z 18.4N 77.9W 45 KT 50 MPH
12H 18/0600Z 18.9N 80.3W 60 KT 70 MPH
24H 18/1800Z 19.4N 83.4W 70 KT 80 MPH
36H 19/0600Z 20.0N 86.7W 75 KT 85 MPH
48H 19/1800Z 20.5N 89.7W 60 KT 70 MPH…INLAND
60H 20/0600Z 20.9N 92.2W 65 KT 75 MPH…OVER WATER
72H 20/1800Z 21.2N 94.8W 75 KT 85 MPH
96H 21/1800Z 21.0N 99.5W 40 KT 45 MPH…INLAND
120H 22/1800Z 21.0N 103.0W 20 KT 25 MPH…POST-TROP/INLAND

HURRICANE watches and warnings are in effect, and the following information is from the NHC advisories:

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Hurricane Warning is in effect for...
* Yucatan Peninsula of Mexico from Cancun to Punta Herrero,
including Cozumel

A Hurricane Watch is in effect for...
* Cayman Islands

A Tropical Storm Warning is in effect for...
* Jamaica
* Southern coast of the Cuban provinces of Santiago de Cuba, Granma,
Las Tunas, and Camaguey
* Cayman Islands
* Yucatan Peninsula of Mexico from north of Cancun to Cabo Catoche
* Yucatan Peninsula of Mexico from south of Punta Herrero to Puerto
Costa Maya

A Tropical Storm Watch is in effect for...
* Southern coast of the Cuban provinces of Ciego de Avila, Sancti
Spiritus, Cienfuegos, Matanzas, and Pinar del Rio, as well as Isla
de la Juventud.

A Hurricane Warning means that hurricane conditions are expected
somewhere within the warning area. A warning is typically issued
36 hours before the anticipated first occurrence of tropical-storm- 
force winds, conditions that make outside preparations difficult or 
dangerous. Preparations to protect life and property should be 
rushed to completion.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area.

Interests elsewhere in the Yucatan Peninsula of Mexico should
monitor the progress of Grace.

Additional watches or warnings may be required tonight.

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

Key messages for Grace can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT2, WMO header WTNT42 KNHC
and on the web at
www.hurricanes.gov/graphics_at2.shtml?key_messages.

WIND: Tropical storm conditions are expected to continue over
portions of Jamaica through early tonight. Tropical storm
conditions are expected along a portion of the southern coast of 
Cuba within the warning area through early tonight, and over the 
Cayman Islands beginning tonight and into early Wednesday. Hurricane 
conditions are possible in the Cayman Islands by early Wednesday. 
Tropical storm conditions are possible along the southern coast of 
Cuba within the watch area tonight and Wednesday. Hurricane 
conditions are expected within the warning area in the Yucatan 
Peninsula of Mexico on Wednesday night with tropical storm 
conditions beginning as early as Wednesday evening.

RAINFALL: The system is expected to produce the following rainfall
amounts:

Over Haiti...an additional 1 to 2 inches of rain with isolated
maximum totals of 15 inches are expected across the southern terrain
areas today. This heavy rainfall will likely cause flash and
urban flooding, along with possible mudslides.

Over far southern Cuba...and additional 2 to 4 inches of rain.
Additional heavy rainfall could lead to flash and urban
flooding, along with possible mudslides.

Over Jamaica, the Cayman Islands, and portions of the Yucatan
Peninsula....3 to 6 inches of rain with isolated maximum totals of
10 inches are expected through Thursday. This heavy rainfall could
lead to flash and urban flooding.

STORM SURGE: A storm surge could raise water levels as high as 1 to
3 ft above normal tide levels in portions of the Cayman Islands.

A dangerous storm surge will raise water levels by as much as 3-5
feet above normal tide levels along the immediate coast near and to
the north of where the center makes landfall in the northeastern
Yucatan Peninsula late Wednesday or early Thursday. Near the
coast, the surge will be accompanied by large and destructive waves.

SURF: Swells generated by Grace will spread westward from Jamaica
to the Cayman Islands, the southern coast of Cuba, and the
Yucatan Peninsula of Mexico. These swells are likely to cause
life-threatening surf and rip current conditions. Please consult
products from your local weather office.

United Nations

CARIBBEAN RADAR IMAGES (LINK)
https://www.barbadosweather.org/Composite/kidbuuComposite_Lionel_displayer2.php?Product=Reflectivity&Sector=fullView&Composite=Sabre&ANISP=700&MAPP=1&PlanetOfTheApes=11254

Given the lateness of the evening, I will not be posting on HENRI.  However, based on analysis this evening, I agree wit the current forecast track,along with the NHC intensity forecast, in that HENRI will become a hurricane.  A Tropical Storm watch is in effect for Bermuda.
HENRI SATELLITE ANIMATIONS
United States
www.barbadosweather.org/Composite/kidbuuComposite Lionel displayer2.php?Product=Reflectivity&Sector=fullView&Composite=Sabre&ANISP=700&MAPP=1&PlanetOfTheApes=11254

NHC FORECAST TRACK
www.hurricanes.gov/graphics at2.shtml?key messages
ATCF 00Z GUIDANCE
Yucatan Peninsula
NHC INTENSITY FORECAST
INIT 17/2100Z 30.4N 64.2W 55 KT 65 MPH
12H 18/0600Z 30.3N 65.5W 60 KT 70 MPH
24H 18/1800Z 30.2N 67.0W 60 KT 70 MPH
36H 19/0600Z 30.2N 68.6W 60 KT 70 MPH
48H 19/1800Z 30.3N 70.0W 60 KT 70 MPH
60H 20/0600Z 31.0N 71.1W 60 KT 70 MPH
72H 20/1800Z 32.0N 71.5W 65 KT 75 MPH
96H 21/1800Z 35.5N 69.6W 70 KT 80 MPH
120H 22/1800Z 39.1N 65.2W 70 KT 80 MPH

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Watch is in effect for...
* Bermuda

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

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

WIND: Tropical storm conditions are possible tonight across Bermuda 
and the nearby waters, particularly to the south of the island.

SURF: Swells generated by Henri are expected to affect Bermuda
during the next day or so. Swells could increase along the
southeast and mid-Atlantic U.S. coasts by the end of the week.
These swells could cause life-threatening surf and rip current
conditions. Please consult products from your local weather office.

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

 



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