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 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #149

Updated: Nov 1

*******Note that forecasts 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.**********


...SUNDAY OCTOBER 31 2021 1:50 AM EDT...

Satellite image as of 1810Z (Oct 30). Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green are in the NHC 2-day tropical weather outlook:

NHC TAFB Surface Analysis 1200Z (Oct 30):

GFS Model Upper-Level Winds 1200Z (Oct 30):

The Atlantic tropics remain buzzing with activity as we end the month of October. See area of interest sections below for multiple areas of interest being monitored for tropical development in the Atlantic basin:

**Area of interest #1...central Atlantic surface cyclone recently upgraded to Subtropical Storm Wanda

**Area of interest #2...tail end of cold front currently crossing the western Caribbean Sea...expected to reach the southern Caribbean Sea in an upper wind environment potentially favoring tropical development within the next couple of days.

**Area of interest #3...Tropical low pressure area in the eastern tropical Atlantic… located south of the Republic of Cabo Verde Islands.


AREA OF INTEREST #1 (RECENTLY UPGRADED TO SUBTROPICAL STORM WANDA)… More recent satellite image of Subtropical Storm Wanda…taken as of 0405Z:

The surface frontal cyclone and upper vortex that was previously in the open north Atlantic has continued to track southeast and is now in the open central Atlantic. Despite its current position over water temps in the low 20s of deg C...the surface cyclone has continued to develop a solid mass of thunderstorms with the aid of the cold de-stabilizing temperatures of the upper vortex. As a result the surface cyclone has acquired enough tropical characteristics to be designated as Subtropical Storm Wanda as of 11 PM EDT.


A portion of the upper ridge that was over eastern Canada has been knocked into the northwest Atlantic by a developing upper vortex over North America. The flow between this upper ridge and amplified northeast Atlantic upper trough has been responsible for the ongoing southeast track of what is now Wanda. The strong upper ridge in the short-term is forecast to funnel some of the cold air associated with the northeast Atlantic upper trough southwestward into the overhead upper vortex. This should slow the warming of the upper vortex which may aid to keep the instability over Wanda. While it is observed that the thunderstorm canopy over Wanda is tilted to the east side of the surface swirl center due to westerly shear from Wanda’s current position beneath the southwest side of the upper vortex… Wanda will have an opportunity in the next 24 hours to re-align with the center of the upper vortex where shear is lower as the vortex is expected to continue accelerating southeast in tandem with Wanda. I am in agreement with the NHC 11 PM EDT advisory on forecasting Wanda to strengthen slightly to 60 mph max sustained winds due to the potential reduction in shear and cold de-stabilizing temps of the upper vortex. I also forecast Wanda to transition to fully tropical as the thunderstorm canopy is showing evidence of cirrus warm core upper outflow which is the mechanism that keeps the strength of a fully-tropical system. I do not anticipate a strength higher than 60 mph max sustained winds however as the upper vortex is forecast to warm just above 1200 dekameters in height at 200 mb by 24 and 48 hours (would prefer to see the 200 mb height of the upper vortex at or below 1200 for more confidence that the upper vortex is cold enough for instability). In addition the forecast track does not take Wanda south of the warm 26 deg C sea surface temperature isotherm where it would not need the help of the cold temps of the upper vortex.


By 48 hours… the northwest Atlantic upper ridge will be making its way into the northeastern Atlantic. The eastern convergence zone of this upper ridge and adjacent eastern Atlantic upper ridge is expected to produce strong surface ridges to the east that will dampen the eastward progress of Wanda. At the same time... the current eastern US upper trough will be approaching from the west… with the flow between the upper trough and surface ridges turning Wanda north. Because this upper trough is likely to approach in an amplified state...it has potential to increase the upper divergence over Wanda and keep shear levels low. However the upper trough is not forecast to be cold enough for thunderstorm generation and tropical development… and in fact is forecast to be warmer than the current overhead upper vortex. Therefore by 72 hours I anticipate Wanda to lose tropical characteristics… however while maintaining strength from the eastern divergence zone of the upper trough.

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

0 Hr Position (0000Z Oct 31)… 50 mph maximum sustained wind subtropical storm centered at 37N-46W

IOH 24 Hr Forecast (0000Z Nov 1)… 60 mph maximum sustained wind tropical storm centered at 32.5N-43W

IOH 48 Hr Forecast (0000Z Nov 2)… 60 mph maximum sustained wind tropical storm centered at 31N-41W

IOH 72 Hr Forecast (0000Z Nov 3)…60 mph maximum sustained wind non-tropical remnant cyclone centered at 32.5N-40W


AREA OF INTEREST #2...The current highly amplified cold core upper trough moving across the eastern United States is expected to drive a surface cold front from its current position in the western Caribbean Sea and into the south-central Caribbean Sea over the next 24 hours. The tail end of this front may evolve into a tropical disturbance supported by the outflow and low shear of the ongoing upper ridge in the western Caribbean. I assign low 10% odds of tropical cyclone development by day 3 as only some model runs show the formation of a defined tropical low pressure... and even those runs do not show tropical cyclone formation. Anything that does develop will likely drift west toward Nicaragua by days 2 and 3 as a steering surface ridge builds over North America in the wake of the amplified upper trough. Odds of development are dropped to 0% by day 4 due to forecast landfall over Nicaragua.

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

IOH 24 Hr Outlook (0000Z Nov 1)… 0% chance of tropical cyclone formation (south-central Caribbean Sea near 12.5N-78W)

IOH 48 Hr Outlook (0000Z Nov 2)… 5% chance of tropical cyclone formation (south-central Caribbean Sea near 12.5N-80W)

IOH 72 Hr Outlook (0000Z Nov 3)… 10% chance of tropical cyclone formation (just offshore of the Nicaragua coast near 12.5N-83W)

IOH 96 Hr Outlook (0000Z Nov 4)… 0% chance of tropical cyclone formation (western Nicaragua near 12.5N-86W)


AREA OF INTEREST #3...A tropical disturbance continues in the eastern tropical Atlantic… consisting of a surface tropical wave with low pressure spin that has been ongoing near 32.5W longitude… and another tropical low pressure spin that has developed further east while well-embedded in thunderstorm bands that have been aided by the upper outflow of tropical upper ridging in the region. It is this eastern tropical low pressure that has been the focus for possible tropical development… especially as warm core upper ridging amplifies over it due to the warm southerly flow occurring on the east side of Subtropical Storm Wanda. Meanwhile the tropical wave and rotation to the west is not expected to develop and will likely weaken while exposed to westerly shear to be continued by the approaching upper vortex associated with Wanda. The tropical wave’s only influence on the tropical low pressure of Interest has been to deflect its track more north… which resulted in its center passing 10N-25W as of 0000Z earlier tonight. As a result… my updated forecast track is adjusted north. The forecast track is west-northwest to northwest toward the surface ridge weakness of Wanda. Even though the overall thunderstorm activity of the tropical low has reduced… I have raised my peak odds of development to 50% as it maintains a small and strong circular area of thunderstorms near the center as of this writing which may be enough for further development. Odds of development are tapered down to 0% by 72 hours as the forecast track eventually takes this system into a belt of shearing upper southwesterly winds to be generated by Wanda’s upper vortex.

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

IOH 24 Hr Outlook (0000Z Nov 1)… 50% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-29W)

IOH 48 Hr Outlook (0000Z Nov 2)… 30% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-33W)

IOH 72 Hr Outlook (0000Z Nov 3)… 0% chance of tropical cyclone formation (eastern tropical Atlantic near 17.5N-36W)


...COMPUTER MODEL SUMMARY...

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

1200Z CMC Model Run...

**For area of interest #1... dives southeast and reaches 32.5N-42W at 60 hours as a possible subtropical storm…turns north-northeast and reaches 43N-37.5W at 120 hours

**For area of interest #2...tail end of front develops into a southern Caribbean tropical low pressure near 10N-81W at 60 hours... tropical low pressure gradually loses defintion thereafter and no development forecast

**For area of interest #3...weakens to a surface trough near 14N-32.5W at 36 hours


1200Z ECMWF Model Run...

**For area of interest #1... dives southeast and reaches 33N-40.5W at 72 hours as a possible subtropical storm…turns north-northeast and reaches 43N-38.5W at 120 hours

**For area of interest #2...tail end of front develops into a southern Caribbean tropical low pressure near 12.5N-79W at 24 hours...tropical low drifts southwest into the Nicaragua/Costa Rica border just after 72 hours

**For area of interest #3... weakens to a surface trough near 15N-32W at 48 hours


1800Z GFS Model Run...

**For area of interest #1... dives southeast and reaches 32.5N-42W at 60 hours as a subtropical storm…turns north-northeast and reaches 46.2N-38.5W at 120 hours

**For area of interest #2... tail end of front develops into a southern Caribbean tropical low pressure near 11.2N-79W at 24 hours… tropical low drifts southwest into the Nicaragua/Costa Rica border just after 66 hours

**For area of interest #3... weakens to a surface trough near 15N-32.5W at 60 hours

1200Z NAVGEM Model Run...

**For area of interest #1... dives southeast and reaches 33.5N-40.5W at 66 hours as a possible subtropical storm… turns north-northeast and reaches 43N-38.5W at 120 hours

**For area of interest #2... tail end of front develops into a southern Caribbean tropical low pressure near 12.5N-81W at 48 hours… tropical low pressure gradually loses defintion thereafter and no development forecast

**For area of interest #3... weakens to a surface trough southwest of the Republic of Cabo Verde Islands by 36 hours

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