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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 

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*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********

...SUNDAY MAY 21 2023 2:11 PM EDT...

Tropical disturbance east-northeast of the Bahamas now highlighted in the National Hurricane Center tropical weather outlook for the Atlantic Basin... temporarily resuming daily birdseye view posts on the Atlantic tropics even though hurricane season does not officially start until June 1st. See area of interest #3 section below for more information.

As done on this site starting last year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development throughout the year... resetting back to #1 at the start of each year. This scheme is so that each area of interest retains a numeric identity from update to update... which reduces confusion when simultaneous areas of interest begin and end when tropical activity increases during the Atlantic Hurricane Season. The current area of interest is tagged #3 as the first couple were tagged earlier in the year as follows:

Northwest Atlantic cyclonic storm with tropical characteristics during mid-January... the National Hurricane Center (NHC) has recently determined that this storm met the persistence criteria to be considered this season's first (subtropical) storm:

Special report from mid-January on the northwest Atlantic storm... did not classify it as the first area of interest at the time as operationally the NHC suggested it would not meet the persistence criteria to be considered a subtropical or tropical cyclone:

Area of Interest #1... potential for subtropical development in the eastern to central Atlantic in late January:

Area of Interest #2... potential for subtropical development in the northern Gulf of Mexico in early April:

The National Hurricane Center has recently expanded their tropical weather outlook to cover the next 7 days (previous product covered through 5 days). On this site will continue with outlooks not exceeding 5 days (120 hours). As of this update I have also begun to list the NHC tropical weather outlook for each area of interest in addition to my outlook for cyclone formation probabilities.

AREA OF INTEREST #3... Hovmoller diagram showing the progression of the upper trough energy (May 17 to 20) that has recently triggered a tropical disturbance east-northeast of the Bahamas ( The yellow circle represents the position of the upper trough energy in each satellite frame:

Satellite imagery of the tropical disturbance east-northeast of the Bahamas over the last 24 hours (May 20 to 21):

Over the last several days computer models have been intermittent in showing potential for subtropical or tropical development in the western Atlantic in association with a low-latitude upper trough that would enter the region from the southeastern United States. The low-latitude upper trough originated while separating from the tail end of a high-latitude upper trough/surface frontal system that is now currently positioned over the north Atlantic and was previously positioned over eastern North America. Initially some model runs suggested subtropical or tropical development supported by the eastern divergence zone of the low-latitude upper trough in the vicinity of the coastal Carolinas around May 19... after which time the models backed off on this solution and later transitioned to a potential subtropical or tropical disturbance northeast of the Bahamas. However I had not begun daily pre-season tropical updates on this system as the models also indicated the disturbance becoming quickly elongated and less tropical while becoming overran by the elongated eastern divergence zone of the next high-latitude upper trough which is now approaching from eastern Northern America as of this writing. However due to the organizing structure of this disturbance over the last 24 hours... the National Hurricane Center (NHC) as of 8 AM EDT is now highlighting it in their weather outlook product for the Atlantic basin while assigning low 10% odds of tropical cyclone formation.

The new disturbance east-northeast of the Bahamas has become characterized by a persistent comma shaped shower and thunderstorm mass... and associated surface trough of low pressure... over the last 24 hours. The east side of the cloud mass has cirrus outflow suggesting sufficient warm core outflow produced by thunderstorm latent heat release to suggest the disturbance is at present more tropical instead of a hybrid subtropical disturbance more reliant on the eastern divergence zone of the low-latitude parent upper trough. As of 1200Z today the NHC TAFB surface analysis suggests a new surface low just northeast of the eastern Bahamas co-located with the hook region of the comma-shaped cloud mass. However the CIMSS 850-mb vorticity product ( shows the maximum mid-level spin is not stacked with the new surface low while displaced further north and is also somewhat elongated instead of circular... and the ASCAT-B and ASCAT-C ascending satellite pass of surface winds ( does not show a fully closed circulation associated with the new surface low. This indicates that the low-level cyclonic structure of this system will need some to organize in order to support tropical cyclone formation... and upper-level winds at present are conducive for this to occur as the eastern divergence zone of the parent low-latitude upper trough will aid in additional thunderstorm generation while at the same time the parent trough is amplified enough to keep westerly wind shear levels low. However upper-level wind conditions in the next 24 hours will quickly become hostile to tropical cyclone formation as the currently approaching high-latitude eastern North America upper trough will dislodge the adjacent Gulf of Mexico upper ridge and hence the parent low-latitude upper trough southeastward... aligning the surface low with the suppressing upper convergence zone on the northwest side of the parent upper trough. Therefore as of this update I continue to forecast a 0% chance of tropical cyclone formation from this system. After 24 hours the approaching high-latitude upper trough from eastern North America is then expected to transition this disturbance into a more elongated and less tropical frontal low pressure system that passes just northwest of Bermuda. Expect increasing rainfall potential from this system across Bermuda through the early part of this upcoming week (over the next 72 hours).

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

IOH 24 Hr Outlook (1200Z May 22)... 0% chance of tropical cyclone formation (western Atlantic near 27.5N-71.5W)

******National Hurricane Center ( official outlook as of 2 PM EDT***************************

Formation chance through 48 hours...10%

Formation chance through 7 days (168 hours)...10%


Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (

0000Z (May 21) CMC Model Run...

**For area of interest #3... surface trough strengthens to surface low northeast of the Bahamas near 24.5N-71.5W at 24 hours... becomes a weaker and elongated low in the vicnity of 26.5N-73W through 48 hours... elongating low passes just west of Bermuda through 84 hours... at 90+ hours north end of elongated low becomes a frontal cyclone while remaining southern part evolves into cold front attached to the cyclone.

0000Z (May 21) ECMWF Model Run...

**For area of interest #3... surface trough evolves into a surface low northeast of the Bahamas near 24N-71.8W at 24 hours... becomes weaker and elongated north-to-south through 72 hours in the vicinity of 72W longitude... north end of elongated low evolves into a frontal cyclone well northwest of Bermuda through 102 hours.

0600Z (May 21) GFS Model Run...

**For area of interest #3... surface troughs strengthens to a surface low northeast of the Bahamas near 25.2N-72.5W at 18 hours... becomes elongated north-to-south through 60 hours while still maintaining a well-defined center near 29.5N-69.5W... well-defined center in the elongated system passes just west of Bermuda at 75 hours and briefly acquires a compact tropical structure just north of Bermuda at 78 hours... at 81+ hours the compact tropical structure quickly loses identity within the remainder elongated outer circulation as this remainder circulation transitions into a frontal cyclone midway between Bermuda and Nova Scotia.

0600Z (May 21) NAVGEM Model Run... Not available at above-mentioned source

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