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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 #22

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


...SATURDAY JUNE 3 2023 2:15 AM EDT...

Despite Tropical Depression Two in the eastern Gulf of Mexico becoming Tropical Storm Arlene... Arlene appears to already be decaying. See Arlene section below for more information. Meanwhile the upper trough that Arlene is embedded within has potential to bring additional rounds of heavy rainfall to Cuba... the Bahamas... Haiti... and the Dominican Republic over the next few days.


For the northeastern Atlantic Ocean... over the next five days the current north-central Atlantic upper vortex will be pushed into the northeastern Atlantic by a warm core upper ridge that develops to its west (this upper ridge will be manifested in the warm sector of a forecast northwest Atlantic frontal cyclone to be gradually generated by divergence zone of the lengthy upper trough Arlene is embedded within). The surface frontal cyclone that is currently associated with the upper vortex has become stacked below the vortex's core where there is a lack of divergence... as such this cyclone will begin to decay. However as the upper vortex shifts east into the northeastern Atlantic... its southeastern divergence zone is forecast to generate a new frontal cyclone midway between the Azores and the Canary Islands. Recent runs of the GFS and ECMWF models suggest the new cyclone could be strong enough with a well-defined (instead of elongated) center to support subtropical development. However water temps in the region are currently at 19 deg C and the 200 mb height of the upper vortex core is forecast to be 1190 dekameters. Would prefer to see more forecast instability thru colder upper air temps (lower 200 mb heights) for these water temps before issuing outlooks on possible subtropical development... therefore I have not done so at this time. Regardless of its eventual structure (non-tropical... subtropical etc)... the forecast cyclone will likely be large enough to bring coastal surf and gusty winds to the Azores and Canary Islands by early next week.


TROPICAL STORM ARLENE... Satellite image of Tropical Depression Two in the eastern Gulf of Mexico strengthening into Tropical Storm Arlene (1611Z Friday June 2):

The upper trough that has been diving southeastward from the east coast of Canada has merged with the eastern US to Gulf of Mexico upper trough... the result being an impressively lengthy upper trough with a southwest-to-northeast tilt (the tilt direction is due to the initial position of all elements in the merger). The lengthy upper trough is becoming quasi-stationary while becoming pinned down by the amplified upper ridge over central North America. Tropical Depression Two has been moving south-southeastward in the northwesterly flow on the back side of the upper trough. Although the depression has been struggling with westerly shear imparted by the upper trough... the displaced thunderstorm activity (on the east side of the circulation) made a comeback early on Friday by re-strengthening and staying close to the center of circulation. As of 2 PM EDT Friday NHC aircraft reconaissance determined that Tropical Depression Two strengthened to Tropical Storm Arlene. The first NHC advisory on this cyclone (5 PM EDT on June 1) suggests this system is a shallow type of tropical cyclone... where the surface circulation and upper-level warm core outflow are below the 200 mb layer of the atmosphere. Therefore using the 200 mb layer of the atmosphere to judge the amount of shear... which is the layer shown in the above birdseye view chart... causes an overassessment of the actual amount of shear affecting Arlene. This may explain how Tropical Depression Two was able to recover and strengthen to Tropical Storm Arlene. However the shear... and also the suppressing upper convergence on the back side of the upper trough... appear to be finally working their magic on Arlene as the tropical storm has lost most of its thunderstorm activity... in fact this is the least amount of activity seen in the circulation since this system was upgraded to a tropical cyclone on June 1. Therefore my forecast... and also the NHC official forecast... call for Arlene to degenerate into a remnant low pressure in the next 24 hours. Regarding the forecast track... because the upper trough has become quasi-stationary as noted in the above remarks... Arlene is forecast to catch up to the axis of the upper trough where the upper flow is more westerly... which should result in the south-southeastward track bending more eastward with time.


Note within the last few days the eastern divergence zone of the upper trough has been producing thunderstorms with pockts of heavy rainfall across the Bahamas... Cuba... and Haiti. As of this writing thunderstorm activity covers Haiti... the western Dominican Republic... and the eastern Bahamas. Note this rainfall is NOT associated with Arlene. Additional heavy rainfall is possible in this region for a few more days as the upper trough has become quasi-stationary. The divergence zone of the upper trough may also trigger a surface trough in this region. However the southwest-northeast tilt of the upper trough will allow for hostile levels of westerly shear in the region... therefore any surface trough that develops here is not expected to undergo tropical development.

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

0 Hr Position (0000Z Jun 3)... 40 mph maximum sustained wind tropical storm centered in the eastern Gulf of Mexico at 25.4N-85.5W

IOH 24 Hr Forecast (0000Z Jun 4)... Remnant low centered just southwest of the Florida Keys and just offshore of northwestern Cuba at 23.8N-82.5W

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

Loss of Tropical Cyclone Status (0000Z Jun 4)... 30 mph maximum sustained wind remnant low centered just offshore of northwestern Cuba at 23.5N-84W


...COMPUTER MODEL SUMMARY...

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


1200Z (Jun 2) CMC Model Run...

**For Tropical Storm Arlene... circulation moves south-southeast toward the northwest coast of Cuba while weakening and loses identity by 42 hours within and loses identity by 42 hours within a larger-scale surface trough becoming established in the region.


1200Z (Jun 2) ECMWF Model Run...

**For Tropical Storm Arlene... circulation moves south-southeast toward the northwest coast of Cuba while weakening and loses identity by 42 hours within a larger-scale surface trough becoming established in the region.


1800Z (Jun 2) GFS Model Run...

**For Tropical Storm Arlene... circulation moves south-southeast while weakening and reaches the northwest coast of Cuba as a remmant low by 30 hours... while becoming a feature supported by the eastern divergence zone of the upper trough in the region the broad remnant low shifts east through the Florida Straits (between Florida peninsula and Cuba) through 54 hours and passes over the northwestern Bahamas through 63 hours... while arcing northeastward the remnant low degenerates into an elongated surface trough midway between the Bahamas and Bermuda through 90 hours.


1800Z (Jun 2) NAVGEM Model Run...

**For Tropical Storm Arlene... circulation moves south-southeast while weakening and reaches the northwest coast of Cuba as a remmant low by 30 hours... remnant low curves east into the Florida Straits (between Florida peninsula and Cuba) where it then loses its identity by 54 hours within larger-scale surface trough becoming established in the region.

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