BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #83

Updated: Aug 19

*******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 AUGUST 18 2021 1:55 AM EDT...

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. Also see remnants of Fred section below for a final update on the former tropical storm that is now a remnant low over the eastern US.


Elsewhere...satellite imagery this past afternoon suggested some signs of organization to the southeast of the Republic of Cabo Verde Islands from the most recent tropical wave of low pressure to exit Africa. However as of tonight this wave has lost thunderstorm activity while the surface inflow of an adjacent wave over interior Africa dominates as seen by the adjacent wave’s eruption of widespread strong thunderstorms tonight. Will monitor this adjacent wave as it moves offshore in the coming days for signs of development… should this occur will add it as an area of Interest.


REMNANTS OF FRED... Since sunrise on Tuesday Fred dropped below tropical storm force while continuing to jog northward inland across the southeastern US. Based on the latest radar the center of rotation of Fred’s remnant low pressure is over eastern Kentucky and remains enhanced by the eastern divergence zone of the upper vorticity over the central US. The track of Fred has been a little more west… so in addition to the Appalachians of the Carolinas and the Virginias the heavy rainfall and flash flood potential spread over eastern Tennessee earlier on Tuesday… and now extends as far west as eastern Kentucky and eastern Ohio. From here… the heavy rain and flash flood risk will shift across the northeastern US over the next day or so as the supporting upper vorticity over the central US makes an eastward shift. This is my final statement on Fred’s remnants as this system is no longer a tropical cyclone.


TROPICAL STORM GRACE... More recent Satellite image of Grace taken at 0420Z:

Grace has awoken from its slumber… finally ramping back up into a tropical storm and making a decent strengthening trend as the center tracked westward away from Haiti… and across the north coast of Jamaica over the last day. The center is continuing a brisk west track and is already about to make a pass just south of the Cayman Islands by the time we move into the morning hours. Due to the storm’s current position… I have shifted the forecast track points west which brings Grace toward the Yucatan and then the Veracruz regions of Mexico a little sooner in the coming days. Later in the forecast period there will be a pair of frontal systems moving through western North America… with the surface steering layer wanting to pull Grace more west-northwest into the surface ridge weakness of the fronts. In the upper layers the vast area of warm upper ridging is forecast to expand in the warm sector of the frontal systems… resulting in upper-level steering wanting to push a strong/tall Grace west-southwest. Even if Grace weakens from a hurricane to a tropical storm while crossing the Yucatan… it could still be strong/tall enough to be coupled to the upper-level steering once it moves out over the Gulf of Mexico waters Also we now have two global models (NAVGEM and GFS) that show a more south angle in the track. Therefore I agree with a south adjustment in track… even for the short-term as Grace has stayed more south in track.


Regarding intensity… Grace has stayed south of the western Atlantic upper vorticity and is now in a vast region of low shear and upper outflow beneath upper-level ridging… a situation that favors Grace much more. The latent heat release of the thunderstorms in Grace may have also played a role in keeping the cool core upper vorticity at bay. Therefore we expect Grace will ramp up to Hurricane strength twice… once before the Yucatan landfall on Thursday… and once before landfall in the Veracruz region of Mexico on late Friday/Saturday. The question now is just how strong of a hurricane? For the first landfall for now I agree with the NHC intensity forecast and nothing higher as the outer thunderstorms dwindled in some recent satellite photos. But with a central band now wrapping back into the center it wouldn’t surprise me if Grace makes a comeback and the short-term intensity forecast requires another upward adjustment. My longer term intensity forecast is a bit lower than my previous and also lower than the NHC as of this writing as the recent adjustments in the forecast track increase land interaction with the Yucatan peninsula… but still has Grace become a hurricane for the second time.


With these forecast updates:

** Interests in Jamaica may see additional heavy rains and flooding for a few more hours from the eastern bands of Grace

** Interests in the Cayman Islands should have finished at this point… tropical storm to hurricane force weather conditions are expected in the coming hours.

** The potential for tropical storm conditions for Cuba has ended. However on the current track, Grace will still bring coastal sea swells to the south coast of Cuba.

** I recommend interests across the northern Yucatan peninsula continue preparing for Grace (conditions to deteriorate on Thursday). Given the latest intensity forecast… preparations should account for possibly severe hurricane force conditions (dangerous coastal sea swells… wind damage potential) as Grace in the short-term could strengthen more than shown in the forecast below.

** Interests in the Mexican provinces of Tamaulipas and Veracruz should be aware of Grace as the storm has potential to make landfall Friday night or Saturday as a hurricane. It appears the most likely landfall region will be central Veracruz. While land interaction with the Yucatan may dampen Grace’s intensity on approach to this region… structural changes are hard to forecast and Grace may still recover quickly from the Yucatan and strengthen more than shown in the forecast below. 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.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (0000Z Aug 18)… 60 mph maximum sustained wind tropical storm centered just west of Jamaica at 18.4N-79.2W

IOH 24 Hr Forecast (0000Z Aug 19)… 85 mph maximum sustained wind hurricane in the northwest Caribbean centered at 19N-85.5W

IOH 48 Hr Forecast (0000Z Aug 20)… 50 mph maximum sustained wind tropical storm centered just offshore of the northwest Yucatan peninsula coast at 20N-91W

IOH 72 Hr Forecast (0000Z Aug 21)… 75 mph maximum sustained wind hurricane centered just offshore of central Veracruz at 20.5N-96.5W

IOH 96 Hr Forecast (0000Z Aug 22)… Remnant low over central Mexico centered at 20.5N-100.5W


TROPICAL STORM HENRI… More recent Satellite image of Henri taken at 0510Z:

Henri has spent much of the last 24 hours intensifying to the south of Bermuda as I previously forecasted as the northerly shear that has been plaguing the organization relaxed as the upper ridging to the west is shifting eastward and beginning to overspread the storm. The forecast track of this system is adjusted south in the short-term due to Henri’s current position. The track is expected to be the continuation of a slow anti-cyclonic loop around the island of Bermuda while pushed around by the eastern US surface ridge as that ridge moves offshore into the northwest Atlantic. The initial slow speed in the track is due to the drag of the Atlantic surface ridge to the east which will try to oppose the force applied by the nearing eastern US surface ridge. By 72 hours the upper vorticity over the north-Central US will be heading into the northwest Atlantic... creating a surface ridge weakness with its eastern divergence zone that should carry Henri north. My longer term forecast points are adjusted more north and west once again as the upper vorticity is forecast to be more amplified… which will provide a more southerly steering flow in the upper levels (which Henri will be coupled to as a strong/tall tropical cyclone) and cause the surface ridge weakness to not be as Far East as previously shown. This brings Henri closer to the northeast US and Atlantic Canada coasts in the long range… something to watch for if this model trend continues.


Regarding intensity… no changes in the short-term due to the excellent performance of the previous forecast. I expect m a ramp up to Hurricane strength as the nearby upper ridging is forecast to continue shifting east over Henri which will help end the shear and produce an excellent upper outflow environment. I have also elevated the longer term intensity as the shear levels will be lower due to the approaching upper vorticity being more amplified… with weakening only shown by day 4 due to cooler waters. Even by day 5 the intensity of Henri as a remnant non-tropical system could be elevated with the supportive divergence zone of the upper vorticity.


On the current track… Henri will no longer bring a threat of winds to Bermuda… but coastal sea swells are a concern. Coastal sea swells and rip currents will also be possible for the US east coast and Atlantic Canada coast should Henri keep its strength as forecast below. The potential for gusty winds on the northeast US coast and Atlantic Canada coasts by days 4 and 5 are uncertain at this time… but certainty will grow if the model results stay the same in the next day or so.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (0000Z Aug 18)…65 mph maximum sustained wind tropical storm centered south of Bermuda at 30N-65.1W

IOH 24 Hr Forecast (0000Z Aug 19)… 80 mph maximum sustained wind hurricane centered southwest of Bermuda at 30.5N-67W

IOH 48 Hr Forecast (0000Z Aug 20)… 95 mph maximum sustained wind hurricane centered in the western Atlantic near 32.5N-69W

IOH 72 Hr Forecast (0000Z Aug 21)… 95 mph maximum sustained wind hurricane centered in the northwestern Atlantic near 37N-69W

IOH 96 Hr Forecast (0000Z Aug 22)… 80 mph maximum sustained wind hurricane centered offshore of the northeast US near 39N-68W

IOH 120 Hr Forecast (0000Z Aug 23)… Frontal cyclone centered just offshore of Maine and Nova Scotia near 42.5N-67W


...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 Tropical Storm Grace... passes over the Cayman Islands at 18 hours… crosses the northeastern Yucatan peninsula as a hurricane at 42 hours… makes landfall as a hurricane over east-central Mexico at 90 hours… rapidly weakens after landfall.

**For Tropical Storm Henri... reaches 31N-72W at 60 hours after which time it turns north in track… weakens to a remnant low near 32.5N-72.5W at 72 hours… remnant low loses closed circulation near 38N-66W at 120 hours

**Strong tropical wave emerges from Africa at 54 hours… features elongated circulation passing 35W longitude at 120 hours


1200Z ECMWF Model Run...

**For Tropical Storm Grace...crosses the Cayman Islands as a high-end tropical storm at 24 hours… makes landfall over the northeast Yucatan at 48 hours as a hurricane… makes landfall as an intense hurricane over east-central Mexico between 72 and 96 hours.

**For Tropical Storm Henri... reaches 31N-72.5W at 72 hours after which time it turns north in track… weakens to a remnant low near 35N-71W at 96 hours.

**Strong tropical wave of low pressure forecast to emerge from Africa at 48 hours... broad low pressure spin of wave passes over the Republic of Cabo Verde Islands between 72 and 96 hours… center of spin located at 16N-35W at 120 hours


1800Z GFS Model Run...

**For Tropical Storm Grace... crosses the Cayman Islands at 15 hours as a hurricane… crosses the northeastern Yucatan peninsula at 39 hours… makes landfall in east-central Mexico near 20N-96W at 93 hours

**For Tropical Storm Henri… attains Hurricane strength and reaches 31N-72.5W at 60 hours after which time it turns north… by 123 hours the hurricane is centered just offshore of Cape Cod Massachusetts

**Strong tropical wave of low pressure forecast to emerge from Africa at 48 hours... broad low pressure spin of wave passes over the Republic of Cabo Verde Islands at 75 hours... center of spin located near 15N-35W at 120 hours


1800Z NAVGEM Model Run...

****For Tropical Storm Grace... crosses the Cayman Islands at 12 to 18 hours while strengthening further… crosses the northeastern Yucatan peninsula at 42 hours at Hurricane strength… makes landfall east-central Mexico near 21N-97W at 90 hours as an intense hurricane.

**For Tropical Storm Henri... weakens to remnant low near 32.5N-71W at 54 hours

**Strong tropical wave of low pressure forecast to emerge from Africa at 66 hours... broad low pressure spin of wave passes over the Republic of Cabo Verde Islands at 102 hours... center of spin located near 17.5N-28W at 120 hours.

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