MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #36
*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...WEDNESDAY JUNE 30 2021 2:35 PM EDT...
See both area of interest sections below for a pair of vigorous tropical waves of low pressure en route to affect the Lesser Antilles and northern Caribbean islands in the coming days. Of note...the eastern of the two tropical waves is at risk of developing into a potentially dangerous hurricane.
Elsewhere...the outflow of a narrow upper ridge running from Texas to the western Gulf of Mexico continues to support thunderstorms and a surface low pressure field over the western Gulf. However satellite animation of low-level clouds suggests the surface rotation remains onshore along the northeastern Mexico coast...and this disturbance could bring heavy rainfall with flash flooding potential over the Mexican provinces of Tamaulipas and Veracruz if the offshore heavy thunderstorm activity spreads onshore. Conditions for additional development here will soon decline as the northeastern Gulf of Mexico upper vortex gets pushed southwest into the heart of the Gulf of Mexico as the Texas portion of the upper ridge amplifies in warm southerly flow ahead of the persistent central US frontal system. The further southwest position of the upper vortex will subsequently suppress upper outflow in the western Gulf.
And finally...a surface tropical wave of low pressure in the northwestern Caribbean Sea in conjunction with the eastern divergence zone of the northeastern Gulf of Mexico upper vortex is producing a north-south broad area of showers and thunderstorms across the northwestern Caribbean and eastern Gulf of Mexico. As discussed in the previous paragraph...the upper vortex is forecast to shift southwestward...which will allow the tropical Atlantic upper ridge to expand northwestward in its wake. Although models do not forecast any development at the present time...it is possible a tropical disturbance develops in the eastern Gulf of Mexico over the next day or so while taking advantage of low shear and outflow beneath the expanding tropical Atlantic upper ridge...and also potentially taking advantage of the eastern divergence zone of the upper vortex as well. Anything that does develop would tend to move northwest around the southwest side of the Atlantic surface ridge.
AREA OF INTEREST #1...After once again becoming disorganized overnight...the westernmost of the vigorous tropical waves of low pressure in the central tropical Atlantic has redeveloped somewhat organized curved thunderstorm bands while moving across the Lesser Antilles as of this morning and early afternoon. With none of the computer models (except the usually less reliable CMC) developing this wave...the NHC has dropped development odds to 0% in their outlook as of this writing. Conditions ahead for this tropical wave will be favorable for development due to warm waters along the forecast track (26+ deg C)...coupled with low shear and upper outflow beneath the tropical upper ridge in the region. The cold core upper vorticity in the western Atlantic will continuously shrink while cut-off from high-latitude cold air...therefore wind shear will remain low even as the tropical wave crosses the Caribbean Sea through day 4. And with the wave producing vigorous thunderstorm bands and moving into the Caribbean where dry Saharan air tends to be less concentrated...I prefer at this time to not entirely go with the models lackluster forecast and thus I only slightly lower my peak odds of development to 20%
The forecast track is due west-northwest as the wave rounds the southwest side of the Atlantic surface ridge. By the end of the 5-day forecast period...the central North American upper trough and its surface cold front will have finally made its way into the western Atlantic...potentially eroding the west side of the Atlantic surface ridge enough for the tropical wave to move more northwest across western Cuba and into the eastern Gulf of Mexico. By day 5...the tropical wave may encounter upper westerly shearing winds in the Gulf of Mexico to be induced by the south side of the upper trough...thus I taper odds of development downward to 10%. On this forecast track...the wave will pass near Haiti...Jamaica...the Cayman Islands...and Cuba over the next few days. All of these land areas could see heavy rainfall and gusty winds even if a tropical cyclone does not form...especially if the wave maintains its current thunderstorm bands while taking advantage of the forecast favorable conditions in the Caribbean Sea. The Dominican Republic may also see similar effects from this tropical wave as the lastest satellite imagery shows the wave is producing a large enough thunderstorm field for the wave to produce impacts well northeast of the wave axis location.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jul 1)...5% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-64.8W)
IOH 48 Hr Outlook (1200Z Jul 2)...15% chance of tropical cyclone formation (just south of eastern Haiti near 17.5N-72W)
IOH 72 Hr Outlook (1200Z Jul 3)...20% chance of tropical cyclone formation (between Jamaica and eastern Cuba near 19N-77.5W)
IOH 96 Hr Outlook (1200Z Jul 4)...20% chance of tropical cyclone formation (just offshore of Cuba's southwest coast near 22N-82.5W)
IOH 120 Hr Outlook (1200Z Jul 5)...10% chance of tropical cyclone formation (southeastern Gulf of Mexico near 25N-87.5W)
AREA OF INTEREST #2...The eastern Atlantic tropical wave of low pressure...located east of area of interest #1...has moved into the central tropical Atlantic while continuing to display an organized spin currently present near 10N-42W. All of the global models are now in agreement on this tropical wave developing at some point within the next five days...and this tropical wave will be in an environment conducive to further development with warm sea surface temperatures and expansive tropical upper ridging with low shear and upper outflow. Given the organized current structure of the wave...the model support...and favorable environment...I have begun a tropical cyclone formation forecast as outlined below which shows specific track and intensity forecast points.
My updated forecast track is faster to the west than the previous as the models agree on a faster-than-average westward track despite showing the wave being of high amplitude and developing. Usually higher amplitude waves move a little bit slower in the atmosphere...but it appears the steering Atlantic surface ridge will be strong and far south enough (while supported by a southern-located upper convergence zone to setup between the north side of the tropical upper ridging and south side of the norhtwest Atlantic upper ridge cell) to push this wave more quickly west. The forecast track bends more north once this system enters the Caribbean Sea while rounding the southwest side of the Atlantic surface ridge. By the end of the 5-day forecast period...the central North American upper trough and its surface cold front will have finally made its way into the western Atlantic...potentially eroding the west side of the Atlantic surface ridge...which will make a north angle in the track all the more likely.
The intensity projections in the CMC and ECMWF models are puzzling...which show this system become a tropical cyclone in the short-term and then dissipate it once it moves in the Caribbean despite very warm waters...low shear...upper outflow...etc. On the other extreme is the bullish GFS which already has this system as an intense hurricane by the time it crosses the southern Lesser Antilles late Friday and into Saturday. Using current observations...we see that there is a narrow swath of dry saharan air to the northwest of this tropical wave and to the east of area of interest #1...and the thunderstorm bands at the core are not particularly strong...with the outer thunderstorm bands biased to the south as the tropical wave is under the south side of the tropical upper ridge where the upper flow tends to be northerly. Therefore in my intensity forecast shown below...I disagree with the GFS and show gradual development into a high-end tropical storm over the next 48 hours as the south-biased thunderstorm bands will not be in a position to protect the core from the dry saharan air lurking to the north. However after this system enters the Caribbean Sea...the north angle in track will bring this system more directly below the tropical upper ridge axis which will allow for a more symmetrical upper outflow and thunderstorm pattern...plus the water temps in the Caribbean Sea are warmer and the dry saharan air concentration tends to be less in this region. This is when I ramp up my intensity forecast to indicate a major hurricane (category 3+) by day 5.
With the lastest forecasts...I recommend interests in the southern Lesser Antilles to begin preparing for tropical storm conditions...with possible hurricane-force conditions...arriving by late Friday and into Saturday. There is the usual longer-term uncertainty with the track and intensity forecast...therefore interests in Haiti and Jamaica should monitor this system carefully as this tropical wave could develop into a potentially dangerous hurricane late this weekend and into early next week.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jun 30)...Tropical low pressure centered over the central tropical Atlantic at 10N-42W
IOH 24 Hr Forecast (1200Z Jul 1)...40 mph maximum sustained wind tropical storm centered over the central tropcial Atlantic at 10.5N-48W
IOH 48 Hr Forecast (1200Z Jul 2)...60 mph maximum sustained wind tropical storm centered east of the southern Lesser Antilles at 11N-55W
IOH 72 Hr Forecast (1200Z Jul 3)...85 mph maximum sustained wind hurricane centered just west of the southern Lesser Antilles near 12.2N-62W
IOH 96 Hr Forecast (1200Z Jul 4)...110 mph maximum sustained wind hurricane centered in the eastern Caribbean Sea at 15N-69W
IOH 120 Hr Forecast (1200Z Jul 5)...135 mph maximum sustained wind major hurricane centered south of southwestern Haiti at 17.2N-74W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...
**For area of interest #1...crosses the Lesser Antilles as an amplified tropical wave at 18 hours...develops into a compact tropical low pressure in the eastern Caribbean Sea at 14N-67.5W at 42 hours...compact tropical cyclone formation shown in central Caribbean Sea near 15.5N-78.8W at 72 hours...makes landfall over southern Belize as a compact hurricane by 114 hours...weakening remnant low located over northern Guatemala at 126 hours.
**For area of interest #2...tropical cyclone formation shown near 12.2N-35.5W at 54 hours...crosses the southern Lesser Antilles at 66 hours while weakening to a remnant but still vigrous low pressure...remnant low crosses Haiti by 96 hours...remnant low turns northwest across eastern Cuba by 108 hours and approaches Andros Island in the western Bahamas by 120 hours.
0000Z ECMWF Model Run...
**For area of interest #1...crosses the Lesser Antilles as a weak tropical wave just before 24 hours...no tropical cyclone formation shown
**For area of interest #2...tropical cyclone formation shown near 10.2N-45W at 24 hours...crosses the southern Lesser Antilles between 48 and 72 hours while weakening back to a tropical wave...tropical wave does not regenerate into a tropical cyclone.
0600Z GFS Model Run...
**For area of interest #1...crosses the Lesser Antilles as a weak tropical wave at 12 hours...no tropical cyclone formation shown
**For area of interest #2...tropical cyclone formation shown near 8N-42W at 12 hours...reaches hurricane strength at 30 hours while passing near 10.5N-47.5W...crosses Barbados as an intense hurricane by 60 hours...crosses the southern Lesser Antilles by 63 hours...makes landfall as an intense hurricane over the southwestern Dominican Republic at 93 hours...weakens quickly to a tropical storm while crossing Haiti by 102 hours...tropical storm makes landfall on southern coast of eastern Cuba at 120 hours.
0600Z NAVGEM Model Run...
**For area of interest #1...crosses the Lesser Antilles as a weak tropical wave at 12 hours...no tropical cyclone formation shown as the tropical wave progresses across the Caribbean
**For area of interest #2...tropical cyclone formation shown near 10N-47.5W at 30 hours...crosses the southern Lesser Antilles by 66 hours...intensifes into a hurricane while passing south of Jamaica at 114 hours...located south of the Cayman Islands as an intense hurricane near 17.5N-80.5W at 126 hours.