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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 #105

*******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...TUESDAY OCTOBER 24 2023 1:37 AM EDT...

The birdseye view chart below has been updated to include the surface and upper air analysis for 1800Z October 23 which were effective at the time the forecasts and discussions below were created.


...TUESDAY OCTOBER 24 2023 12:35 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 within the next several hours.


Hurricane Tammy has curved northwestward and then northeastward away from the northern Lesser Antilles islands... the next land area likely to be affected by Tammy would be Bermuda and by late this week and the weekend. See Tammy section below for more information.


Elsewhere noting the following disturbances in the Atlantic basin:

(1) The southern Caribbean tropical low pressure has become tropical depression twenty-one... the depression however is already making landfall in Nicaragua and thus is not expected to become a named tropical storm... see tropical depression twenty-one section below for more details.

(2) A tropical wave of low pressure has moved quickly westward into the southern Lesser Antilles. This system may evolve into a bonafide tropical disturbance to the south of Tammy over the next few days... see area of interest #49 section below for more details.


HURRICANE TAMMY... Over the last 48 hours Tammy has lifted northwestward and then north-northeastward away from the northern Lesser Antilles while now chasing the western Atlantic surface ridge weakness associated with recent frontal systems that have departed the United States. The northwest leg of the journey put the hurricane further west of previous forecasts and closer to the neighboring eastern Caribbean upper vorticity. Therefore instead of intensifying further as previously expected... Tammy has gradually weakened to a minimal hurricane with 75 mph maximum sustained winds due to southerly shear imparted by the upper vorticity. The updated forecast track points are adjusted south and west of the previous due to the hurricane's current position relative to the prior forecast... however the forecast track philosophy remains the same as follows... (1) the current north and northwest Atlantic surface frontal systems and north half of the associated upper trough are expected to leave Tammy behind... (2) the western convergence zone of the northern upper trough fragment followed by the convergence zone of upper vorticity that ejects from the current north Canada upper vortex is expected to build a surface ridge to the north of Tammy that would prevent the storm from continuing northeastward out to sea... (3) a westward turn is expected in the long range due to the combined effects of the surface ridge and southwestern upper trough fragment which evolves into a cut-off upper vortex with time. For intensity... noting that Tammy appears better organized in recent satellite frames perhaps as the latent heat release of its thunderstorms have weakened the aforementioned shearing eastern Caribbean upper vorticity. However I forecast some weakening over the next 24 hours as Tammy moves into stronger southwesterly shear associated with the aforementioned upper trough. By 48 hours the shear over Tammy reduces while upper divergence simultaneously increases as the aforementioned southwestern upper trough fragment evolves into a cut-off upper vortex... and so I forecast Tammy to have some recovery in its strength. The combination of water temps below 26 deg C and ingestion of cooler drier air associated with the upper vortex should cause Tammy to begin losing tropical characteristics by 72 hours... and weakening is shown as the storm whirls into the northern part of the upper vortex where upper divergence is less.


Regarding impacts to land areas:

(1) Coastal surf reaching the shores of the northeastern Caribbean Isalnds (northern Lesser Antilles... Virgin Islands... and Puerto Rico) should reduce as the hurricane continues to lift northward and away from the region.

(2) The latest forecast track projections continue to suggest Tammy making a westward hook toward Bermuda in the long-range. Coastal surf will likely begin for Bermuda by Thursday... with gusty winds possible by this weekend.

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

0 Hr Position (0000Z Oct 24)... 75 mph maximum sustained wind hurricane centered in the western Atlantic at 22.5N-63.6W

IOH 24 Hr Forecast (0000Z Oct 25)... 70 mph maximum sustained wind tropical storm centered in the western Atlantic at 25N-60.5W

IOH 48 Hr Forecast (0000Z Oct 26)... 75 mph maximum sustained wind hurricane centered in the central Atlantic at 29N-58W

IOH 72 Hr Forecast (0000Z Oct 27)... 70 mph maximum sustained wind tropical storm centered in the central Atlantic at 33N-58W

IOH 96 Hr Forecast (0000Z Oct 28)... Remnant non-tropical cyclone centered east-northeast of Bermuda at 33N-61W

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

Peak Strength (0000Z Oct 25)... 85 mph maximum sustained wind hurricane centered in the western Atlantic at 24.7N-60.8W

Loss of Tropical Cyclone Status (0000Z Oct 27)... 65 mph maximum sustained wind non-tropical cyclone centered in the central Atlantic at 31.1N-59.7W


TROPICAL DEPRESSION TWENTY-ONE... The tropical low pressure that has been parked over the southern Caribbean Sea maintained enough organized thunderstorm activity to become upgraded to Tropical Depression Twenty-One as of 5 PM EDT Monday. Low shear and outflow beneath a regional tropical upper ridge cell aided in the genesis of this latest Atlantic basin tropical cyclone. The blocking surface ridge that was over the Gulf of Mexico and northern Central America has become replaced by a further-north surface ridge over the eastern US which is now pushing the depression's center of circulation into the east coast of Nicaragua. Because the depression has already lost its core of thunderstorms in recent hours it is not expected to strengthen into a named tropical storm... and dissipation due to landfall with Nicaragua is forecast over the next 24 hours. As such this is my planned final statement on this system on this blog.


Based on the latest satellite imagery... small pockets of thunderstorms are ongoing in the circulation which may lead to incidents of heavy rainfall across Nicaragua... Costa Rica... western Panama... Honduras... and El Salvador.

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

0 Hr Position (0000Z Oct 24)... 30 mph maximum sustained wind tropical depression centered just offshore of east-central Nicaragua at 12.4N-83.4W

IOH 24 Hr Forecast (0000Z Oct 25)... Dissipating surface low centered over west-central Nicaragua at 12.4N-86.5W

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

Loss of Tropical Cyclone Status (1200Z Oct 24)... 30 mph maximum sustained wind remnant low centered over east-central Nicaragua at 13.1N-84.2W


AREA OF INTEREST #49... A low-latitude tropical wave of low pressure has continued westward toward the southern Lesser Antilles under the influence of the deep-layer ridge now over eastern Atlantic. The CIMSS 850 mb vorticity product confirms a low-level area of rotation just south-southwest of Barbados in association with this tropical wave (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Going forward this system is expected to drift slowly north in the vicinity of the Lesser Antilles island chain and near 60W longitude due to the surface ridge weakness associated with Tammy and while transitioning into a surface trough supported by the southeastern divergence zone of the elongated upper vortex that will be interacting with Tammy (the current eastern Caribbean upper vorticity will be merging with the elongated upper vortex... more info on the upper vortex is in the above Tammy forecast discussion). By days 4 and 5 this system would then likely bend more westward in track as the forecast track for Tammy and its associated surface ridge weakness hooks westward. Regarding odds of tropical cyclone formation... this system has lost vigorous thunderstorm activity and therefore I have lowered peak development odds to 10%. I have reserved peak development odds for the longer range as the cold core upper vortex begins to weaken from prolonged isolated from high-latitude cold air which would reduce the regional southerly wind shear.


So far not much rainfall has occurred across the Lesser Antilles in association with this system. Should this disturbance redevelop widespread thunderstorms... periods of heavy rain could occur across parts of the island chain within the next few days.

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

IOH 24 Hr Outlook (0000Z Oct 25)... 0% chance of tropical cyclone formation (just northwest of Barbados near 14N-60W)

IOH 48 Hr Outlook (0000Z Oct 26)... 0% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 16N-60W)

IOH 72 Hr Outlook (0000Z Oct 27)... 0% chance of tropical cyclone formation (east-northeast of the northern Lesser Antilles near 19N-60W)

IOH 96 Hr Outlook (0000Z Oct 28)... 10% chance of tropical cyclone formation (northeast of the northern Lesser Antilles near 20N-61W)

IOH 120 Hr Outlook (0000Z Oct 29)... 10% chance of tropical cyclone formation (north of the northern Lesser Antilles near 21N-63W)

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

Not in the official outlook


...COMPUTER MODEL SUMMARY...

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


1200Z (Oct 23) CMC Model Run...

**For Hurricane Tammy... moves north-northeast and reaches 27N-60W at 60 hours... subsequently turns northwest and then west and reaches 30N-70W at 120 hours

**For Tropical Depression Twenty-One... not shown in 0-hour initialization and no development shown

**For area of interest #49... no development shown


1200Z (Oct 23) ECMWF Model Run...

**For Hurricane Tammy... moves north-northeast and reaches 27.5N-58.5W at 60 hours... subsequently turns northwest and then west while gradually weakening and passes just south of Bermuda at 108 hours and reaches 30.8N-67.5W at 120 hours

**For Tropical Depression Twenty-One... not shown in 0-hour initialization and no development shown

**For area of interest #49... no development shown


1800Z (Oct 23) GFS Model Run...

**For Hurricane Tammy... moves northeast and reaches 29N-57.5W at 57 hours... subsequently turns northwest into the waters just east-northeast of Bermuda and reaches 33.5N-60.5W at 108 hours... track then reverses to a northeastward course and reaches 34N-60W at 120 hours

**For Tropical Depression Twenty-One... not shown in 0-hour initialization and no development shown

**For area of interest #49... moves north-northwest across the Lesser Antilles and evolves into a better-defined surface trough near 21N-65W by 120 hours


1800Z (Oct 23) NAVGEM Model Run...

**For Hurricane Tammy... moves north-northeast and reaches 25.5N-61.5W at 54 hours... subsequently turns northwest and then west and reaches 30N-71.5W at 120 hours.

**For Tropical Depression Twenty-One... not shown in 0-hour initialization and no development shown

**For area of interest #49... no development shown

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