MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #87 (Weekend Edition)
*******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.**********
...SUNDAY AUGUST 22 2021 9:35 AM EDT...
Satellite image as of 0320Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:
NHC TAFB Surface Analysis 1800Z:
GFS Model Upper-Level Winds 1800Z:
See Grace and Henri sections below for an update on both Atlantic tropical systems… both are currently or are forecast to bring impacts to land areas in the coming days. See area of interest #1 and #2 sections below for an update on the latest tropical wave activity in the east Atlantic.
Elsewhere... a tropical wave of low pressure was producing tremendous thunderstorm activity overnight over Western Africa and has some banding features as it moves offshore… will watch to see if this wave becomes an area of interest in the coming days. In addition… models have converged on developing the currently inactive wave East of the Lesser Antilles as the wave moves into the central Caribbean and encounters an expanding upper ridge with low shear and upper outflow to develop in the wake of the west Atlanfic upper vorticity near the Bahamas as the vorticity weakens while remaining cut-off from high-latitude cold air. If these model trends continue… will consider adding this wave as another area of interest in my next full update on the Atlantic tropics.
REMNANTS OF GRACE… Grace and its thunderstorms rapidly fizzled into a broad low pressure spin over central Mexico within the last 24 hours. However as the broad spin has neared the west coast of Mexico… its west side has seen an eruption in tremendous thunderstorm activity along the west coast and offshore waters. Upper-level winds remain favorable as Grace is still under an expansive upper ridge with low shear and outflow… and there is a high chance of Grace regenerating into an eastern Pacific tropical cyclone just south of the Baja California peninsula over the next day or so where it could generate coastal sea swells that reaches the south side of the peninsula. Because Grace is no longer an Atlantic feature… I will not be forecasting it… instead only making additional remarks on it in the intro section of this blog and in future updates to the home page bulletins of this site. For more info on the remnants of Grace… refer to the eastern Pacific products on the NHC site… hurricanes.gov (hurricanes dot gov).
HURRICANE HENRI (RECENTLY DOWNGRADED TO TROPICAL STORM HENRI)… Henri for much of the last 24 hours became a hurricane offshore of the US East coast… but as the storm is now making landfall near the Rhode Island/Massachusetts border it has weakened to a still impactful high end tropical storm. The tropical storm for some of the last 24 hours had lost its traditional tropical appearance with only some thunderstorms bands on its south side enhanced by the divergence zone on the east side of the upper vorticity just to the west. However a tropical core of thunderstorms is back in action as Henri is now making landfall.
The upper vorticity was able to knock Henri and its landfall point further to the East than yesterday’s forecast. But make no mistake… Henri will not take the traditional route to the northeast… instead it will get whirled west further inland into the northeast US the next 24 hours while swung around by the north side of the amplified upper vorticity. As such… here are the expectations from Henri:
**Tropical Storm force conditions (gusty winds with some damage potential… coastal sea swells) as far west as southeast New York (including the New York City metro area)…and also for Massachusetts… Rhode Island… southern Vermont.. southern New Hampshire… Connecticut… and Long Island New York
** Heavy rains with flooding potential are possible in the above-mentioned region and also northern Vermont.. northern New Hampshire… and Maine.
** Coastal sea swells will reach Maine and as Far East as Nova Scotia.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0600Z Aug 22)… 75 mph maximum sustained wind hurricane centered just offshore of the northeast US at 40.1N-71.2W
IOH 24 Hr Forecast (0600Z Aug 23)… Gale-Force frontal cyclone centered at the New York/Connecticut/Massachusetts border at 42.2N-73.5W
AREA OF INTEREST #1… The tropical wave of low pressure that was in the eastern Atlantic is now in the central Atlantic near 12.5N-42.5W as of this writing… while the adjacent wave to the east has become the focus of in the NHC tropical weather outlook (see area of interest #2 section below for more info on the adjacent wave). However I am continuing this wave as an area of interest as it maintains an area of rotating thunderstorms. Although the dry Saharan air layer is currently strong… it is also more towards the north… perhaps allowing for an opportunity for this wave to develop South of the dry air in a low shear and upper outflow environment beneath the tropical upper ridge axis in the region. However I maintain low 10% development odds as the thunderstorm activity has not become any better organized. The forecast track bends more north at days 4 and 5 due to a surface ridge weakness to be induced by the divergence zone of an upper vortex near the Bahamas to coalesce from the remnants of the current west Atlantic upper vorticity string. I lower odds of development to 5% by day 5 as the forecast track brings the wave close to Hispaniola (Haiti and the Dominican Republic) where disruptive land interaction is possible. Also during this time models have converged on another disturbance developing in the Caribbean to the west-southwest… so this wave could also be competing for surface inflow with that disturbance by day 5. There is no guarantee of notable impacts to the northeast Caribbean Islands at this time as the wave currently only has low odds of development… and also none of the current model runs develop this wave.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Aug 23)… 0% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-48.5W)
IOH 48 Hr Outlook (0600Z Aug 24)… 10% chance of tropical cyclone formation (central tropical Atlantic near 13.2N-54.5W)
IOH 72 Hr Outlook (0600Z Aug 25)… 10% chance of tropical cyclone formation (Lesser Antilles near 13.7N-60.5W)
IOH 96 Hr Outlook (0600Z Aug 26)… 10% chance of tropical cyclone formation (northeastern Caribbean Sea near 16N-65.5W)
IOH 120 Hr Outlook (0600Z Aug 27)… 5% chance of tropical cyclone formation (southwest coast of the Dominican Republic near 18N-71.5W)
AREA OF INTEREST #2… A tropical wave of low pressure in the eastern tropical Atlantic is currently passing 31W longitude and features as of this morning on its southeast side an increasingly defined low pressure spin near 14N-31W with thunderstorms banding features. The NHC Outlook product and computer models suggest this wave has some development potential while moving west-northwest into the open central Atlantic. The north angle in track is expected due to a surface ridge weakness being induced by the divergence zones of some of the current west Atlantic upper vorticity string and also the current North Atlantic upper trough. By day 4 even though the surface ridge weakness closes… some of the west Atlantic upper vorticity string will coalesce into a vortex near the Bahamas whose divergence zone will continue a surface ridge weakness to the west… and thus a north angle in track is still expected. The steering forecast becomes more erratic and fuzzy by day 5 as the upper trough of the current central Canada frontal low will be in the North Atlantic… potentially driving a cold front that creates a narrow surface ridge weakness that traps this system into a slow north drift. If this forecast for this weakness shifts however… the forecast track by day 5 may need adjustments.
Due to the increasing definition of the surface low pressure spin as noted in the above paragraph…. my odds of development are higher than the NHC as of this writing. The models also show some of the west Atlantic upper vorticity string coalescing into a nearby upper vortex to the west. The upper vortex may prove to be helpful rather than disruptive by creating an upper divergence zone on its east side as it also retrogrades westward out of the way due the current west Atlantic upper ridging forecast to expand across the mid-latitudes of the Atlantic… which would prevent the upper vortex from shearing this system. Also the upper vortex is forecast to gradually weaken while cut-off from high-latitude cold air… and this system is forecast to end up underneath the low shear and upper outflow of the mid-latitude upper ridging later in the forecast period. In regards to the dry Saharan air… the southerly flow on the northeast side of this tropical wave has created a visible clearing in the dry air by pushing the dry air northward and away… which is also favorable for the seedling surface low pressure spin on the south side of the wave.
IOH 24 Hr Outlook (0600Z Aug 23)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 16.5N-36W)
IOH 48 Hr Outlook (0600Z Aug 24)… 20% chance of tropical cyclone formation (central tropical Atlantic near 18.8N-42W)
IOH 72 Hr Outlook (0600Z Aug 25)…30% chance of tropical cyclone formation (central Atlantic near 22N-48W)
IOH 96 Hr Outlook (0600Z Aug 26)…40% chance of tropical cyclone formation (central Atlantic near 26N-55W)
IOH 120 Hr Outlook (0600Z Aug 27)… 50% chance of tropical cyclone formation (central Atlantic near 27N-55W)