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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 #34

Updated: Jul 20, 2023

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


...WEDNESDAY JULY 19 2023 5:10 PM EDT...

Tropical Storm Don is expected to curve westward and then northwestward across the open central and northwestern Atlantic over the next few days while potentially strengthening... see Don section below for more information. Elsewhere now monitoring two new additional areas for possible tropical development in the Atlantic basin in the days ahead as follows:

(1) The National Hurricane Center has introduced an eastern Atlantic tropical wave of low pressure into their tropical weather outlook. This is the fourteenth Atlantic tropical area of interest tracked on this site this year... see area of interest #14 section below for more information.

(2) A surface trough of low pressure moving away from the US east coast and across the northwestern Atlantic has developed a better-defined center... and may become a short-lived tropical cyclone before arriving into cooler waters offshore of Atlantic Canada in 48 hours. This is the fifteenth Atlantic tropical area of interest tracked on this site this year... see area of interest #15 section below for more information.


TROPICAL STORM DON... Don continues to wander around in the open central Atlantic. The tropical storm is maintaining a small core of gradually strengthening thunderstorm activity while aligned with an area of aiding split flow upper divergence between the back (northwest) side of the upper trough in the region and front (southeast) side of the northwest Atlantic deep-layer ridge. The tropical storm has been largely moving southward today and now more recently is hooking west-southwestward while it rounds the southeast side of the deep-layer ridge. This track has allowed it to reach slightly warmer 25 deg C waters which may also be contributing to the gradual strenghtening of the thunerstorm core.


Going forward Don and the upper trough in Don's environment will continue to be influenced by the deep-layered ridge as the ridge slowly shifts east as a typical amplified mid-latitude feature. While the northeastern part of the upper trough is forecast to also drift eastward... the southwestern part is forecast to move westward around the south side of the deep-layer ridge as a cut-off upper vortex and eventually become streteched north-south once it moves around the southwest side of the ridge. Don itself will soon turn directly westward... northwestward... and then northeastward while rounding the south and then western sides of the passing deep-layer ridge. Due to Don already hooking more westward at its current position I have nudged the short-term forecast track more northward. The GFS is trending with a stronger deep-layer ridge for the long range which may dampen the long term northeastward acceleration of Don into the open north Atlantic... and therefore the long range track is nudged westward with a slower forward speed. In the short-term Don may strengthen slightly due to the split flow upper divergence mentioned in the prior paragraph. Then by 24 and 48 hours the forecast track below moves Don westward and away from the split flow upper divergence and into a neutral (no divergence or convergence) upper flow in the north side of the cut-off upper vortex and south side of the deep-layer ridge... and so for that timeframe I forecast a minimal tropical storm in this less conducive upper air pattern. By 60 hours the forecast track then puts Don in supportive split flow upper divergence between the north side of the cut-off upper vortex and southwest side of the deep-layer ridge... and by 72+ hours Don is forecast to be near or over more favorable 26 deg C waters and underneath the western side of the deep-layer ridge where low shear and upper outflow may help Don further in a tropical manner. Because the forecast track continues to bring Don into this more favorable environment... I have raised the intensity forecast for that timeframe. To finish off the 5-day forecast... I project Don to gradually weaken in the low shear environment and also lose tropical characteristics by 120 hours as Don moves northeastward across markedly cooler waters east of Newfoundland. If Don retains sufficient strength as it passes by Newfoundland... surf induced by its circulation could reach the eastern shores of Newfoundland in the 4 to 5 day timeframe.


Update as of 5 PM EDT... Don has strengthened to 45 mph maximum sustained winds. The latest NHC intensity forecast now also brings the tropical storm to a forecast peak strength of 60 mph maximum sustained winds.

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

0 Hr Position (1200Z Jul 19)... 40 mph maximum sustained wind tropical storm centered at 33.9N-39.6W

IOH 24 Hr Forecast (1200Z Jul 20)... 40 mph maximum sustained wind tropical storm centered at 33.5N-42W

IOH 48 Hr Forecast (1200Z Jul 21)... 40 mph maximum sustained wind tropical storm centered at 35N-46W

IOH 72 Hr Forecast (1200Z Jul 22)... 60 mph maximum sustained wind tropical storm centered at 38N-50.5W

IOH 96 Hr Forecast (1200Z Jul 23)... 50 mph maximmum sustained wind tropical storm losing tropical characteristics while centered at 42.5N-51W

IOH 120 Hr Forecast (1200Z Jul 24)... Remnant low centered east-southeast of Newfoundland at 46N-49W

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

Peak Strength (1200Z Jul 20)... 50 mph maximum sustained wind tropical storm centered at 33.9N-41.8W

Loss of tropical cyclone status (1200Z Jul 24)... 40 mph maximum sustained wind non-tropical remnant cyclone centered in the north Atlantic at 47N-43W


AREA OF INTEREST #14... In the eastern tropical Atlantic... a tropical disturbance is emerging consisting of an east-west elongated region of thunderstorms around 10N latitude supported by the outflow of a tropical upper ridge in the region. Embedded in this activity is a tropical wave of low pressure near 25W longitude that recently emerged from western Africa. The westward speed of the tropical wave has slowed down due to the surface ridge weakness caused by Tropical Storm Don... however once the tropical storm accelerates northwestward and away and the surface layer of the current northwest Atlantic deep-layer ridge approaches the westward speed of the tropical wave is expected to increase over the next five days. Computer models runs over the last few days have intermittently suggested the tropical wave may develop into a tropical cyclone... and the NHC as of today has introduced the tropical wave as an area of interest for possible development in their tropical weather outlook. Negative factors against development include dry saharan air and the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) showing that regional low-level low pressure/spin is currently elongated due to the elongated region of thunderstorms and upper outflow mentioned above. This means that the tropical wave will not develop unless it fights off the dry air and develops a well-defined low pressure center within the elongated low-level low pressure field. As the southwest part of the current central Atlantic upper trough breaks off into a cut-off upper vortex that moves westward and away around the aforementioned deep-layer ridge... the regional tropical upper ridge is forecast to expand which will provide a larger area of low wind shear and upper outflow that may help the tropical wave later overcome the negative factors. I agree with the NHC in low long-term 20% odds of tropical cyclone formation given the negative factors and currently low computer model support showing development... odds will be adjusted in future updates as needed pending trends in future model runs and/or observations.

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

IOH 24 Hr Outlook (1200Z Jul 20)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-26.5W)

IOH 48 Hr Outlook (1200Z Jul 21)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-28W)

IOH 72 Hr Outlook (1200Z Jul 22)... 5% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-31W)

IOH 96 Hr Outlook (1200Z Jul 23)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-36W)

IOH 120 Hr Outlook (1200Z Jul 24)... 20% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-41W)

******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*****************************

Formation chance through 48 hours...0%

Formation chance through 7 days (168 hours)...20%


AREA OF INTEREST #15... The surface trough of low pressure offshore of the eastern United States... formally a surface cold front driven by the current broad eastern Canada surface frontal low... is continuing northeastward across the northwestern Atlantic while steered by the west side of the current northwest Atlantic deep-layer ridge. On satellite pictures the surface trough continues to be defined by a north-south axis of thunderstorm activity... and as of 1200Z earlier today satellite imagery and the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) suggest a better-defined low pressure center (near 37N-66W) has developed along the trough. As a result I have introduced this system as an area of interest for possible tropical development. The better-defined low pressure center has likely developed due to the maximum of split flow upper divergence between southwesterlies on the west side of the northwest Atlantic deep-layer ridge and northwesterlies on the east side of the upper ridge axis that has been offshore of the eastern US. I assign low 20% peak odds of tropical cyclone formation as this system will only have 24 more hours before moving into cooler waters below 26 deg C non-conducive to tropical development and as the better-defined center appears to stil have some north-south elongation in satellite pictures instead of being more circular and consolidated.

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

IOH 24 Hr Outlook (1200Z Jul 20)... 20% chance of tropical cyclone formtion (northwest Atlantic near 40.5N-60.5W)

IOH 48 Hr Outlook (1200Z Jul 21)... 0% chance of tropical cyclone formation (offshore of south-central Newfoundland near 45N-57.5W

******National Hurricane Center (hurricanes.gov) official outlook as of 2 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 (Jul 19) CMC Model Run...

**For Tropical Storm Don... curves west and then northwest to 39.5N-49W through 84 hours while gradually weakening... continues north and then northeast into cooler waters through 120 hours where it weakens to a remnant trough near 48N-45W

**For area of interest #14... no development shown

**For area of interest #15... compact surface low becomes better defined near 39N-64W at 18 hours... makes landfall over south-central Newfoundland at 48 hours as a less tropical feature over cooler water.


0000Z (Jul 19) ECMWF Model Run...

**Not available at above-mentioned source


0600Z (Jul 19) GFS Model Run...

**For Tropical Storm Don... curves west-northwest to 36N-49W through 72 hours while strengthening into a high-end compact tropical storm... passes southeast of Newfoundland through 120 hours as a compact tropical storm gradually losing strength and tropical characteristics over cooler waters

**For area of interest #14... no development shown

**For area of interest #15... compact surface low becomes better defined near 39N-64W at 18 hours... dissipates over cooler waters offshore of southwestern Newfoundland at 60 hours


0600Z (Jul 19) NAVGEM Model Run...

**For Tropical Storm Don... curves west and then northwest to 39N-46.5W through 78 hours while weakening to a remnant low... remnant low continues north-northeast to 47.5N-42.5W through 120 hours where it weakens further to a trough.

**For area of interest #14... no development shown

**For area of interest #15... no development shown

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