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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 #122

*******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.*********


...TUESDAY NOVEMBER 14 2023 3:15 PM EDT...

The thunderstorm activity in the southern Caribbean Sea has developed into a surface trough of low pressure located in the vicinity of northeastern Nicaragua and the east tip of Honduras. This system is expected to accelerate northeastward across the northern Caribbean islands... southeastern Bahamas... and then toward Bermuda through day 5 while bringing heavy rainfall... see area of interest #53 section below for more information.


Elsewhere... a frontal low is expected to develop in the vicinity of the Florida peninsula and northwestern Bahamas over the next 48 hours. The supporting upper trough may be amplified enough to produce low enough wind shear and high enough upper divergence for thunderstorm activity and tropical characteristics of this feature... see area of interest #54 section below for more information.


AREA OF INTEREST #53... The persistent thunderstorm activity over the south-central Caribbean Sea has evolved into a surface trough of low pressure located in the vicinity of the northeast coast of Nicaragua and eastern tip of Honduras. This initial position is northwest of my previous forecast and current global model guidance envelope... and my updated one below is adjusted accordingly. Going forward the forecast track calls for northeastward movement in deep-layer southwesterly flow ahead of a southern stream upper trough and associated surface frontal low to approach from the Gulf of Mexico (more information on the southern stream upper trough and frontal low is in the area of interest #54 section below). I have lowered my peak odds of tropical cyclone formation to 10% for the following reasons:

(1) The northward adjusted track places the disturbance closer to the incoming upper trough and associated hostile southwesterly shear. Although the 200 mb analysis in the above birdseye view chart shows this disturbance is currently tucked under a regional tropical upper ridge where wind shear should be currently low... the thunderstorm activity is already biased to the northeast side of the surface trough which indicates southwesterly shear... perhaps below the 200 mb layer of the atomsphere... could already be starting.

(2) This disturbance is at risk of becoming an elongated tropical low with multiple centers... instead of a single center needed for tropical cyclone formation... due to the large size and elongated nature of the incoming upper trough’s divergence zone... in particular as it merges with a higher-latitude upper trough that moves across North America from its current Alaska position by late in the 5-day forecast period.


Regardless of tropical cyclone formation or not... the following impacts to land areas are anticipated:

(1) Per the latest satellite imagery... rainfall across Nicaragua and Honduras appears to have come to an early end as southwesterly shear across this disturbance may already be in progress as noted above.

(2) An area of thunderstorms and heavy rainfall has developed just west of the Cayman Islands... associated with divergence ahead of the incoming southern stream upper trough. This area of heavy rainfall should transfer eastward across the islands over the next 24 hours.

(3) By later this week and into the weekened... a corridor of heavy rainfall with possible flooding concerns is expected across Jamaica... eastern Cuba... the southeastern Bahamas... and Haiti. Rainfall is also possible across the Dominican Republic... however with the latest forecast track shown below rainfall totals here could end up being less than the aforementioned land areas. With the current forecast... the corridor of heavy rainfall shifts into Bermuda by Sunday.

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

IOH 24 Hr Outlook (1800Z Nov 15)...0% chance of tropical cyclone formation (offshore and east-northeast of Honduras near 15.5N-82W)

IOH 48 Hr Outlook (1800Z Nov 16)... 10% chance of tropical cyclone formation (just west-northwest of Jamaica and south of the Cayman Islands near 19N-80W)

IOH 72 Hr Outlook (1800Z Nov 17)... 10% chance of tropical cyclone formation (just offshore of the northeastern Cuba coast near 21.5N-76.2W

IOH 96 Hr Outlook (1800Z Nov 18)... 10% chance of tropical cyclone formation (western Atlantic near 25N-71W)

IOH 120 Hr Outlook (1800Z Nov 19)... 0% chance of tropical cyclone formation (vicinity of Bermuda near 32N-65W)

*****National Hurricane Center (hurricanes.gov) official outlook as of 1 PM EDT***************************

Formation chance through 48 hours... 20%

Formation chance through 7 days... 70%


AREA OF INTEREST #54... The divergence zone of a southern stream upper trough currently over the south-central United States has been supporting a surface frontal low that has been pivoting eastward across the northern Gulf of Mexico. The surface pressure gradient between the frontal low and strong surface ridge over eastern North America as of this writing is producing gusty winds and coastal surf for the Gulf of Mexico coastal regions of Florida... Alabama... Mississippi... and southeastern Louisiana. A shield of heavy rainfall as of this writing covers southern Georgia... southern Alabama... and northern Florida with more scattered showers extending as far west as Mississippi and Louisiana.


Over the next 48 hours the eastward speed of the upper trough is expected to be faster than the surface frontal low while the frontal low is pinned down by the adjacent surface ridge... this will result in the current frontal low dissipating under the lack of divergence beneath the upper trough axis while divergence on the east side of the upper trough kicks up a new frontal low in the vicinity of the Florida peninsula and northwestern Bahamas. This should result in an eastward shift of the heavy rainfall across the remainder of Florida and the northwestern Bahamas during this timeframe... as well as an eastward transfer of the gusty winds and coastal surf into the southeastern US coastal region and offshore Atlantic waters. The upper trough may be amplified enough through 72 hours to have an upper divergence maximum to concentrate thunderstorm activity and surface pressure falls to make the replacement frontal low feature a well-defined instead of elongated center and tropical characteristics... and the GFS model in recent runs has hinted at this. However I assign a low 10% chance of tropical cyclone formation as the other global models do not agree with the GFS. By 96+ hours the upper trough currently position over Alaska merges with the southern stream upper trough... with the combined lengthy upper trough accelerating this system northeastward into cooler waters... as such my outlook for tropical cyclone formation ends at 96 hours with 0% development odds. This system is likely to strengthen into a non-tropical frontal cyclone supported by the divergence zone of the combined upper trough by then... with the cyclone expected to produce coastal surf for the mid-Atlantic and northeastern US coastline... as well as Atlantic Canada... by this weekend. Atlantic Canada is the most likely land area to see notable gusty winds from this phase of the system... however gusty winds for the mid-Atlantic and northeastern US coast cannot be ruled out should the cyclone develop and track a little closer to shore.

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

IOH 24 Hr Outlook (1800Z Nov 15)... 0% chance of tropical cyclone formation (offshore of the west-central Florida peninsula coast near 27.5N-83.8W)

IOH 48 Hr Outlook (1800Z Nov 16)... 10% chance of tropical cyclone formation (offshore of the east-central Florida peninsula coast near 28N-79.8W)

IOH 72 Hr Outlook (1800Z Nov 17)... 10% chance of tropical cyclone formation (offshore of the Carolinas near 32.5N-75.5W

IOH 96 Hr Outlook (1800Z Nov 18)... 0% chance of tropical cyclone formation (southeast of Cape Cod Massachusetts near 39.5N-68.5W)

*****National Hurricane Center (hurricanes.gov) official outlook as of 1 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/).


0000Z (Nov 14) CMC Model Run...

**For area of interest #53... becomes a better-defined but broad tropical low in the central Caribbean near 15N-79W at 90 hours... moves northeast across Jamaica through 114 hours and then breaks up into two centers (one over the southeastern Bahamas and one just south of Haiti) through 126 hours... northern center quickly loses its identity along cold front to the north shortly therafter while southern center moves northeast across Hispaniola (Haiti/Dominican Republic) through 138 hours... southern center misses ridge weakness associated with cold front and begins to meander north of Puerto Rico (near 23N-66W) by 168 hours while coming under the influence of a strong surface ridge that builds behind the front

**For area of interest #54... frontal low develops over the northwestern Bahamas at 78 hours... intensifies into a frontal cyclone that approaches the eastern tip of Nova Scotia through 126 hours


0000Z (Nov 14) ECMWF Model Run...

**For area of interest #53... becomes a better-defined but north-south elongated and broad tropical low in the central Caribbean near 15.5N-79.5W through 78 hours... moves north-northeast across Jamaica... eastern Cuba... and the southeastern Bahamas through 102 hours shortly after which time it loses identity to developing frontal system to the north.

**For area of interest #54... frontal low develops over the southeast coast of Florida at 60 hours... by 120 hours the frontal low while located offshore of the Carolinas loses its identity to a pair of frontal cyclones (one just southwest of Bermuda and one offshore of Massachusetts)


0600Z (Nov 14) GFS Model Run...

**For area of interest #53... becomes a better-defined but broad tropical low in the south-central Caribbean Sea near 12.5N-80W at 54 hours... while featuring multiple centers the tropical low moves across Jamaica... eastern Cuba... Hispaniola (Haiti and the Dominican Republic)... and southeastern Bahamas through 111 hours... tropical low transitions into a strengthening frontal cyclone while located south of Bermuda and near 28N-66W at 132 hours... remnant frontal cyclone loses identity to another frontal cyclone that develops to the north through 147 hours

**For area of interest #54... frontal low develops between southeast Florida and northwestern Bahamas at 51 hours... strengthens into a circular and possibly subtropical or tropical cyclone just north of the northwestern Bahamas through 66 hours... center of possible subtropical or tropical cyclone passes just offshore of the North Carolina Outer Banks through 90 hours... transitions into an enlarging and intensifying frontal cyclone centered just offshore of Massachusetts through 105 hours... frontal cyclone makes landfall at the Maine/New Brunswick border at 111 hours which then moves across New Brunswick and into southeastern Quebec through 120 hours


0600Z (Nov 14) NAVGEM Model Run...

**For area of interest #53... becomes a better-defined but broad tropical low in the south-central Caribbean Sea near 12.5N-79W at 54 hours... moves north-northeast across Jamaica and eastern Cuba through 84 hours and then across the southeastern Bahamas through 96 hours... shortly after that time loses identity to frontal cyclone to the north

**For area of interest #54... frontal low develops just north of the northwestern Bahamas at 66 hours... develops into an elongated frontal cyclone offshore of North Carolina through 96 hours... the intensifying frontal cyclone then makes landfall at the Maine/New Brunswick border just before 114 hours with the center then located over the northwest corner of the Gulf of St Lawrence by 120 hours

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