*******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.**********
...SATURDAY AUGUST 21 2021 1:04 AM EDT...
Satellite image as of 0300Z. 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 1200Z:
GFS Model Upper-Level Winds 1200Z:
See Grace and Henri sections below for an update on all active tropical cyclones in the Atlantic basin. Both are currently or are forecast to bring impacts to land areas in the coming days. See area of interest #1 section below for an update on the tropical wave in the east Atlantic.
Elsewhere...models continue to converge on forecasting another vigorous wave emerging from Africa in about 3 days… this wave may become another area of Interest.
MAJOR HURRICANE GRACE...Grace has continued to intensify impressively in the southwestern Gulf of Mexico as documented in special update posts #85A and #85B. This is due to the warm water (29 to 30 deg C) while Grace is also under vast Gulf of Mexico upper ridging featuring low shear and upper outflow… and also while the inner core structure has improved while an eye has become defined in infrared Satellite pictures tonight. Aircraft recon has found Grace is now a category 3 hurricane with 120 mph maximum sustained winds… and this is unfortunate as Grace is now on the verge of landfall in Veracruz where its guaranteed to be a harrowing night.
The previous forecast track has once again done excellent… so I have made no changes to it tonight. The frontal low advancing into central Canada from the central US will want to make Grace move west-northwest toward its surface ridge weakness. In the upper layers the vast area of warm Gulf of Mexico upper ridging is expanding in the warm sector of the frontal low… resulting in upper-level steering wanting to push the strong/tall structure of Grace west-southwest. The net result has been and will continue to be a straight west track into Veracruz and inland provinces… with some south angle in the track possible from the upper-level steering as the models keep hinting at.
With these forecast updates:
**Interests in Veracruz should have long finished preparing for Grace by now. If you like in or near the communities of Naranjos… Tuxpan… Tecolutla… and Nautla… stay sheltered indoors to protect yourself from highly damaging Hurricane force winds. If you live at the coast and are prone to storm surge hopefully you have relocated to more inland higher ground. There is also potential for wind damage inland across northern Puebla as Grace will need time to weaken after landfall… and the potential for gusty winds may spread as far west as Tlaxcala and eastern Hidalgo.
** There is potential for a strong post-landfall rain event with flood potential inland across the provinces of Tlaxcala… Hidalgo… northern Puebla… Mexico… and the Federal District on Saturday. Gusty winds may spread inland across northern Puebla as Grace will take some time to lose its winds after landfall.
**As alluded to in the above discussion… upper-level winds may try to push Grace or it’s moisture more south around or just after landfall time. Heavy rains and flooding potential may therefore also spread into northern Oaxaca… southern Puebla… and Morelos.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Aug 21)… 120 mph maximum sustained wind major hurricane centered just offshore of Veracruz at 20.7N-96.3W
IOH 24 Hr Forecast (0000Z Aug 22)… Remnant low over central Mexico centered at 20.5N-100.5W
TROPICAL STORM HENRI… Henri has still not been able to strengthen to a hurricane just yet… and remains just below hurricane strength. This appears to be due to the fact Henri has remained just south of the west Atlantic upper ridge axis where some northerly shear has been affecting the storm… but there are signs Henri is moving into lower shear directly below the axis as the thunderstorms have become more stacked with the center in recent hours. Therefore it is fairly certain Henri will become a hurricane shortly.
Henri has made the long-awaited north turn in the west side of the steering Atlantic surface ridge… but has done so about 1 degree west longitude of previous forecasts. The implication is that Henri is closer to the approaching eastern US upper vorticity…which increases the storm’s potential to amplify the cool core upper vorticity as the west side of the storm will more easily be able to pull the cool air associated with the upper vorticity southward. The result is the forecast track around landfall time in the northeast US (Sunday) is shifted south and west as Henri whirls around the northeast side of the more amplified upper vorticity… and even whirls into the center of the upper vorticity and meanders a bit under the upper vorticity after the landfall.
Regarding intensity… due to Henri still not being a hurricane… I agree with the NHC lowering the forecast peak intensity a tad to 85 mph max sustained winds. As Henri loses tropical character over cooler water and on approach to landfall on Sunday… I still forecast hurricane force intensity from tremendous supporting divergence expected on the east side of the amplified upper vorticity.
With these Forecast updates:
**Coastal sea swells and rip currents are expected for Bermuda… the US east coast… and Atlantic Canada coast in particular toward Nova Scotia.
**Interests in southeastern New York (including the New York City metro area)… northeast New Jersey… Massachusetts… Rhode Island… southern Vermont.. southern New Hampshire… Connecticut… and Long Island New York should continue preparing for possible tropical Storm to Hurricane force conditions. In addition to the wind… coastal storm surge is a concern. Heavy rains with flooding potential are possible in this region and also northern Vermont.. northern New Hampshire… and Maine.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Aug 21)… 70 mph maximum sustained wind tropical storm centered in the western Atlantic at 32.3N-73.5W
IOH 24 Hr Forecast (0000Z Aug 22)… 85 mph maximum sustained wind hurricane centered offshore of the northeast US at 37.5N-73W
IOH 48 Hr Forecast (0000Z Aug 23)… Hurricane-Force frontal cyclone centered just east of the New York/Connecticut border at 41.5N-73.5W
AREA OF INTEREST #1… Based on the latest night time infrared satellite animation… the area of rotation associated with the east Atlantic tropical wave of low pressure appears to be near 12.5N-35W. Although the dry Saharan air layer is 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. I have lowered peak odds of development to 10% as the thunderstorm activity is considerably weaker and less organized. The forecast track bends more north at day 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. There is no guarantee of notable impacts to the northeast Caribbean Islands at this time as the wave only has low odds of development at this time.
Of note… the NHC forecast track is notably north of my track. The models show this wave being overtaken by and absorbed into the adjacent wave to the east currently located near the Republic of Cabo Verde Islands. The merged wave is then shown to have a large circulation whose north end becomes trapped into a surface ridge weakness to be induced by some of the current west Atlantic upper vorticity string and also the current upper trough entering the Atlantic from east Canada as that trough amplifies while entering the Atlantic. However given that this wave is maintaining independence from the adjacent wave to the east… I do not forecast this scenario and thus forecast this wave to escape the surface ridge weakness while the adjacent wave to the east potentially becomes the one who interacts with the weakness… and so my forecast track at this time is more to the south. Of note… the model support showing the north apex of the adjacent wave to the east developing has increased despite the presence of the dry Saharan air to the north… as the models show a surface low intensifying at the apex with the support of the eastern divergence zone of a central Atlantic upper vortex that coalesces from the remains of the current west Atlantic upper vorticity string. If this scenario occurs and/or the NHC shifts their Outlook product toward the adjacent wave to the east… I will be marking the adjacent wave as a separate area of Interest from this wave… especially if this wave maintains its separation from the adjacent wave.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Aug 22)… 0% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-41W)
IOH 48 Hr Outlook (0000Z Aug 23)… 5% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-47W)
IOH 72 Hr Outlook (0000Z Aug 24)… 10% chance of tropical cyclone formation (central tropical Atlantic near 13N-53W)
IOH 96 Hr Outlook (0000Z Aug 25)… 10% chance of tropical cyclone formation (just east of the Lesser Antilles near 13.5N-59W)
IOH 120 Hr Outlook (0000Z Aug 26)… 10% chance of tropical cyclone formation (eastern Caribbean Sea near 16N-64W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run...
**For Hurricane Grace… makes landfall in east-central Mexico near 22.2N-97.5W at 18 hours… weakens very rapidly after landfall
**For Tropical Storm Henri... reaches Hurricane force just prior to making landfall in southeast New York at 54 hours… thru 84 hours weakens to a remnant low while stalled over southeast New York… weak remnant low turns northeast back over water and passes just south of Nova Scotia by 120 hours.
**For area of interest #1… no development shown as a wave to the east overtakes this wave by 30 hours… the north end of the overtaking wave develops a low pressure spin at its north end near 20.2N-39W at 72 hours… low pressure weakens to a trough shortly thereafter and reaches 30N-52.5W at 120 hours.
**Strong tropical wave forecast to emerge from Africa at 60 hours… spin of wave passes thru the Republic of Cabo Verde Islands at 84 hours… original spin dissipates while the wave develops a new spin further southwest that reaches 10N-35W at 120 hours.
**Tropical waves currently in the eastern Caribbean coalesce into a broad tropical low pressure spin east Belize by 168 hours… development suggested in the long range.
0600Z ECMWF Model Run...
**For Hurricane Grace… makes landfall over east-central Mexico near 20.5N-96.5W at 24 hours…after landfall it weakens very rapidly.
**For Tropical Storm Henri... attains Hurricane strength offshore of the northeast US by 48 hours near 39.5N-72.5W while aided by the eastern divergence zone of the incoming amplified upper vorticity to the west… weakens to a remnant low after landfall over Long Island New York and Connecticut by 72 hours.
**For area of interest #1… no development shown as a wave to the east overtakes this wave by 24 hours… tropical development suggested at the north end of the overtaking wave near 18.5N-39W at 72 hours (data after 72 hours not available at above-mentioned source)
** Strong tropical wave forecast to emerge from Africa at 72 hours (data after 72 hours not available at above-mentioned source)
1800Z GFS Model Run...
**For Hurricane Grace… makes landfall in east-central Mexico near 20N-96W at 15 hours…after landfall it weakens very rapidly.
**For Tropical Storm Henri… attains hurricane strength in the next 3 hours… at 45 hours makes landfall over Long Island New York and Connecticut… thru 72 hours weakens to a remnant low near the Massachusetts/New York border while stalled beneath upper vorticity… after that time the remnant low moves east-northeast back of water… remnant low weakens to a surface trough over western Nova Scotia at 96 hours.
**For area of interest #1… no development shown as a wave to the east overtakes this wave by 12 hours… the overtaking wave loses its spin while passing 41W longitude at 72 hours.
** Strong tropical wave forecast to emerge from Africa at 72 hours… no development shown as wave loses closed circulation not long after entering Atlantic.
1800Z NAVGEM Model Run...
****For Hurricane Grace... weakens to a tropical storm near 20N-96W while making landfall in east-central Mexico over the next 12 hours… weakens very rapidly after landfall
**For Tropical Storm Henri...despite moving over cooler waters it strengthens further just before landfall in the northeast US due to the support of the incoming amplified upper vorticity to the west… makes landfall at the Connecticut/Rhode Island border at 48 hours… whirls west into southeast New York and underneath the upper vorticity where it weakens to a remnant low by 66 hours… after that time the remnant low moves east-northeast back of water… remnant low passes south of Nova Scotia by 120 hours.
**For area of interest #1…no development shown as a wave to the east overtakes this wave by 24 hours… the large broad spin of the overtaking wave moves west-northwest and reaches 20N-54W at 120 hours where it weakens to a surface trough… in long range (thru 168 hours) tropical cyclone formation from surface trough suggested south of Bermuda.