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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 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #99

Updated: Oct 15, 2023

*******Note that forecast 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.*********


...UPDATE...SUNDAY OCTOBER 15 2023 12:40 PM EDT...

The birdseye view chart below has been updated to include the surface and upper air analysis for 0000Z October 14 which were effective at the time the forecasts and discussions below were created.


Sean in the central tropical Atlantic has weakened to a tropical depression while encountering suppressive upper convergence on the southeast side of the ongoing central Atlantic upper ridge. The vigorous tropical wave of low pressure following behind Sean (tagged as area of interest #45 in the update below) is also moving into the central tropical Atlantic but has not yet become a tropical cyclone... however upper winds remain favorable for its development and it still could become a tropical cyclone in the days ahead while moving toward the Lesser Antilles islands.


...SATURDAY OCTOBER 14 2023 6:30 AM EDT...

Note the usual surface and upper air analysis are not included in the above chart to ensure a more timely release of this update… those parts of the chart will be added later today.


For the tropical latitudes of the Atlantic Ocean to the east of the Lesser Antilles… Tropical Storm Sean is expected to weaken due to unfavorable upper winds in the short-term... but could find more favorable upper winds in the long-term... see Sean section below for more information. To the east of Sean... monitoring an organizing tropical wave of low pressure following behind which could also take advantage of more favorable upper winds in the long-term... see area of interest #45 section below for more information. Interests in the Lesser Antilles should be aware of the system tagged as area of interest #45 as it could move into the islands as a potentially strong tropical cyclone just after day 5.


For the northwestern Caribbean Sea... the frontal cyclone currently over the central US will drive the tail end of a surface cold front into the region through day 5. Enough tropical upper ridging with low shear and outflow may persist over the region to potentially convert the tail end of the front into a tropical disturbance... as such another tropical area of interest may emerge in the northwestern Caribbean Sea within the next five days.


TROPICAL STORM SEAN... Sean's westward track has continued to have some north angle while gravitated to the surface ridge weakness associated with the current central Atlantic surface low and additional frontal low now zipping into the central Atlantic. Since my previous update Sean actually ended up strengthening slightly to a peak of 45 mph maximum sustained winds… but then weakened back to a minimal tropical storm with 40 mph max sustained winds once its thunderstorms became suppressed by passage directly below the regional upper vorticity axis where upper divergence is lacking. Abruptly since around 11 PM EDT this evening Sean has fired a small area of thunderstorms covering its center which is allowing the tropical storm to hang on. This could be a sign the cool core upper vorticity axis is beginning to weaken and split in half while remaining isolated from high-latitude cold air… with Sean perhaps finding a small area of upper outflow between the emerging upper vorticity halves that has allowed it to re-develop the small area of thunderstorms. However recent global model runs insist Sean will weaken to a remnant low soon while the storm encounters oppressive upper convergence on the southeast side of the central Atlantic upper ridge… and I also continue to forecast this too given the negative upper wind outlook. Noting in the long range the central Atlantic warm core upper ridge is forecast to amplify in warm southerly flow ahead of what is now the frontal cyclone over central North America as that frontal cyclone later moves into the Atlantic. The eastern Atlantic surface ridge is forecast to retrograde westward while aligning with the southeastern convergence zone of the amplifying upper ridge... resulting in a deep-layer ridge. Eventually what is left of Sean will be turned more westward across the open central Atlantic by the deep-layer ridge... with low shear and outflow in the upper layers of the ridge potentially aiding Sean's remnants. So even though Sean could dissipate in the short-term... whatever is left of Sean may need to be watched in the long term.


Update as of 6 AM EDT… the above-mentioned small core of shower and thunderstorm activity has begun to collapse.

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

0 Hr Position (0000Z Oct 14)… 40 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 15.1N-42.9W

IOH 24 Hr Forecast (0000Z Oct 15)… Remnant low centered in the central tropical Atlantic at 17N-45.5W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT***************************

Loss of Tropical Cyclone Status (1200Z Oct 15)... 30 mph maximum sustained wind remnant low centered in the central tropical Atlantic at 17.5N-46.2W


AREA OF INTEREST #45... The eastern Atlantic tropical wave of low pressure following behind Tropical Storm Sean has seen a notable increase in organized thunderstorm activity as the regional string of upper vorticity that was shearing this system has begun to weaken from prolonged isolation from high-latitude cold air. Going forward a central Atlantic deep-layer ridge is expected to materialize as discussed in the above Tropical Storm Sean section... and at the same time the weakening upper vorticity string is expected to split into two upper vortices. This system and the pair of upper vortices will continue westward in tandem while pushed around by the deep-layer ridge. This outlook means this system will likely be in a favorable upper air environment over time while parked in low shear and upper outflow between the pair of upper vortices... with the inflow into the vortices potentially enhancing the eastern and western outflow of this system. Given the current healthy organization of this system and favorable upper wind outlook that lies ahead… I have begun a tropical cyclone formation forecast with specific track and intensity forecast points as outlined below. I cap the 5-day intensity forecast at top-end category 1 hurricane strength as there are still some global model runs that do not develop this system while suggesting it gets entangled with the eastern of the two upper vortices which would allow the vortex to disrupt it with shear and/or outflow suppression.


I recommend that interests in the Lesser Antilles be aware of this system as it has potential to move into the islands as a strong tropical cyclone just after day 5.

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

0 Hr Position (0000Z Oct 14)... Tropical low centered in eastern tropical Atlantic at 9N-29.5W

IOH 24 Hr Forecast (0000Z Oct 15)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 9.5N-34.5W

IOH 48 Hr Forecast (0000Z Oct 16)... 50 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 10N-39.5W

IOH 72 Hr Forecast (0000Z Oct 17)... 70 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 10.5N-44.5W

IOH 96 Hr Forecast (0000Z Oct 18)... 85 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 11N-49.5W

IOH 120 Hr Forecast (0000Z Oct 19)… 95 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 11.5N-54.5W

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************

Formation chance through 48 hours... 40%

Formation chance through 7 days... 80%


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).


1200Z (Oct 13) CMC Model Run...

**For Tropical Storm Sean... weakens to a remnant low near 16N-43W at 12 hours... remnant low dissipates near 20N-47.5W at 60 hours

**For area of interest #45... tropical cyclone formation suggested near 12.5N-39.5W at 84 hours... tropical cyclone strengthens while moving westward to 13.8N-49W through 120 hours


1200Z (Oct 13) ECMWF Model Run...

**For Tropical Storm Sean... weakens to a remnant trough near 17N-45W at 24 hours

**For area of interest #45... no development shown


1800Z (Oct 13) GFS Model Run...

**For Tropical Storm Sean... weakens to a remnant low near 16N-44W at 21 hours... remnant low dissipates near 19.5N-53.5W at 81 hours

**For area of interest #45... tropical cyclone formation suggested near 11N-36W at 87 hours... tropical cyclone strengthens while reaching 12.5N-41.2W through 120 hours


1800Z (Oct 13) NAVGEM Model Run...

**For Tropical Storm Sean... weakens to a remnant low near 17N-45W through 30 hours... remnant low accelerates westward and reaches 20N-60W through 120 hours

**For area of interest #45... tropical cyclone formation suggested near 10.5N-34W at 48 hours... becomes an intense hurricane while reaching 14N-49.5W through 120 hours

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