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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 #57

*******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 AUGUST 19 2023 8:45 AM EDT...

The Atlantic tropics remain busy while a series of tropical waves of low pressure spanning from the central Atlantic to Africa... supported by the outflow of a lengthy tropical upper ridge... are being monitored for signs of tropical cyclone formation. See area of interest  #20... #21... #23… and #24 sections below for more information. Elsewhere... the tropical wave of low pressure currently in the western Caribbean may later take advantage of more favorble upper winds in the Gulf of Mexico... see area of interest #22 section below for additional details. 


Note the forecasts below were completed as of 0000Z earlier today. However not much has changed with each area of interest since then.


AREA OF INTEREST #20... The tropical low pressure in the low-latitudes of the central Atlantic has moved west-northwest to 15N-46W as of 0000Z. The increase in the north angle of the track has been due to a fujiwhara-type interaction with area of interest (AOI) #24 to the west. Therefore the updated forecast track has been adjusted northward. After 24 hours the track is forecast to bend further northward due to the following... (1) what remains of the current upper vorticity in the western Atlantic is forecast to coalesce into an upper vortex whose eastern divergence zone weakens the western part of the Atlantic surface ridge... (2) as this system nears the upper vortex it could also be pulled northward by the vortex... especially if this system goes on to become a stronger/taller feature... (3) although the current eastern Canada frontal system and upper trough are not expected to affect the steering of this system... a second similar system from central Canada is forecast to break into the western Atlantic by day 4 and add to the western Atlantic surface ridge weakness. Regarding odds of tropical cyclone formation... I have not raised my peak odds above 40% as model support showing development of this feature has reduced and this system remains vulnerable to dry Saharan air to the north as light northerly shear being induced by the regional tropical upper ridge is keeping thunderstorms biased to the southern half of the circulation. Noting this system may reach a lower shear environment by 24 hours as it passes directly below the upper ridge axis... and this is when I assign the peak development odds. After that time this system moves into westerly shear on the south side of the aforementioned western Atlantic upper vortex through 96 hours... followed by westerly shear at 120 hours imparted by upper vorticity arriving from the southeastern US that gets kicked toward this system by the above-mentioned large upper trough that moves into the western Atlantic from central Canada. The tapered down odds of development after 24 hours in the outlook below are a reflection of the increasing westerly shear.


Should this system go on to develop... coastal surf generated by this system may reach the northern Lesser Antilles just after the weekend.

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

IOH 24 Hr Outlook (0000Z Aug 20)... 40% chance of tropical cyclone formation (central tropical Atlantic near 17N-51W)

IOH 48 Hr Outlook (0000Z Aug 21)... 30% chance of tropical cyclone formation (central tropical Atlantic near 19N-55W)

IOH 72 Hr Outlook (0000Z Aug 22)... 10% chance of tropical cyclone formation (northeast of the northern Lesser Antilles near 21N-57.5W)

IOH 96 Hr Outlook (0000Z Aug 23)... 10% chance of tropical cyclone formation (western Atlantic near 23N-60W)

IOH 120 Hr Outlook (0000Z Aug 24)... 10% chance of tropical cyclone formation (western Atlantic near 25N-60.5W)

****** National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT****************************

Formation chance through 48 hours...30%

Formation chance through 7 days (168 hours)...30%


AREA OF INTEREST #21... The eastern Atlantic tropical wave of low pressure... which continues to feature a large gyre of showers and thunderstorms… has continued to become better organized while also seeing an increase in its thunderstorms. Therefore its potential to become a tropical cyclone is increasing. As of 0000Z the center of the gyre was located near 16N-34W… or west of the previous forecast… and the updated one shown below is adjusted accordingly. This system through 72 hours should continue to have a northward angle in its westward track due to the ridge weakness associated with the current northeast Atlantic frontal cyclone… followed by the same surface ridge weakness that Area of Interest #20 (AOI #20) will be bending northwards toward. Between 72 and 96 hours the track is accelerated westward... with less of a northward angle... as this system bumps into what will be remaining of the Atlantic surface ridge during that timeframe. The track then bends north again by 120 hours while turning into the surface ridge weakness that AOI #20 will be entangled in. Regarding odds of tropical cyclone formation... I have once again raised peak development odds since special update #56A to 70%… now in agreement with the NHC outlook as of this writing. I drop odds below this peak after 24 hours as this system likely struggles with westerly shear while nearing the current mid-latitude eastern Atlantic upper vorticity. After 72 hours the upper winds become favorable again for this system as it moves away from the shearing upper vorticity… and moreover by 120 hours the upper vortex in the western Atlantic shifts east toward this system as an amplified upper trough whose eastern divergence zone potentially enhances this system. I begin to creep development odds upward by 120 hours due to the more favored upper wind projection for that timeframe.

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

IOH 24 Hr Outlook (0000Z Aug 20)... 70% chance of tropical cyclone formation (eastern tropical Atlantic near 17.5N-37W)

IOH 48 Hr Outlook (0000Z Aug 21)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 19N-39W)

IOH 72 Hr Outlook (0000Z Aug 22)... 50% chance of tropical cyclone formation (central tropical Atlantic near 20.5N-42W)

IOH 96 Hr Outlook (0000Z Aug 23)... 50% chance of tropical cyclone formation (central Atlantic near 22N-47W)

IOH 120 Hr Outlook (0000Z Aug 24)... 60% chance of tropical cyclone formation (central Atlantic near 26N-51W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************

Formation chance through 48 hours...70%

Formation chance through 7 days (168 hours)...70%


AREA OF INTEREST #22... A large Caribbean tropical wave of low pressure continues to traverse westward… now arriving into the western Caribbean. The southwest edge of the current Atlantic surface ridge is expected to push the wave west-northwest across the remainder of the Caribbean and into the Gulf of Mexico. By the end of the 5-day forecast period an amplified upper trough will be moving into eastern Canada from central Canada... with the western convergence zone of this trough building an eastern North America surface ridge. The southwest side of this ridge will continue the west-northwest trajectory of the tropical wave toward the Texas/Mexico border region. The north apex of the tropical wave may later take advantage of  a more favorable low shear and upper outflow environment associated with the Gulf of Mexico upper ridge cell (currently the upper ridge cell has been squashed into only the southeast corner of the Gulf by the current southeastern US upper vorticity... however the upper ridge cell is forecast to later recover as the vorticity retrogrades west and away under the influence of a central US upper ridge cell). Due to increasing computer model support among the usually more reliable GFS and ECMWF models… I have raised peak odds of tropical cyclone formation to 30% for this update. Interests in northeastern Mexico and southern Texas should be increasingly aware of possible impacts such as heavy rainfall and gusty winds which would arrive by Tuesday.

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

IOH 24 Hr Outlook (0000Z Aug 20)… 0% chance of tropical cyclone formation (just south of western Cuba near 21N-83.5W)

IOH 48 Hr Outlook (0000Z Aug 21)… 0% chance of tropical cyclone formation (south-central Gulf of Mexico near 23N-89W)

IOH 72 Hr Outlook (0000Z Aug 22)… 15% chance of tropical cyclone formation (western Gulf of Mexico near 24.5N-94W)

IOH 96 Hr Outlook (0000Z Aug 23)… 30% chance of tropical cyclone formation (far southern Texas coast near 26.5N-97.5W)

IOH 120 Hr Outlook (0000Z Aug 24)… 0% chance of tropical cyclone formation (inland just northeast of the Texas/Mexico border near 28N-99.5W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************

Formation chance through 48 hours...0%

Formation chance through 7 days (168 hours)...50%


AREA OF INTEREST #23... Animation of METEOSAT satellite imagery (https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) suggests a tropical wave of low pressure continues across western Africa with its maximum rotation arriving to 10N-11.5W as of 0000Z… and more recent satellite imagery suggests the maximum rotation is already nearing the west coast of Africa. Therefore the updated forecast track points in the outlook below have been adjusted westward. This wave also has development potential as it later moves into and across the eastern tropical Atlantic... due to the persistent favorable low shear and upper outflow of the regional tropical upper ridge to remain in place over the next several days. The westward forecast track has some northward angle overall as the wave of forecast to move toward the surface ridge weakness caused by Area of Interest #21. I have raised peak odds of tropical cyclone formation to 25% in this update as the associated thunderstorm activity has some signs of organization. Note that this wave may produce heavy rain and gusty winds for the Republic of Cabo Verde Islands later this weekend and into Monday.

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

IOH 24 Hr Outlook (0000Z Aug 20)…0% chance of tropical cyclone formation (offshore of western Africa near 10.5N-19.5W)

IOH 48 Hr Outlook (0000Z Aug 21)… 10% chance of tropical cyclone formation (just southeast of the Republic of Cabo Verde Islands near 12N-22.5W)

IOH 72 Hr Outlook (0000Z Aug 22)… 25% chance of tropical cyclone formation (just west-southwest of the Republic of Cabo Verde Islands near 14N-26W)

IOH 96 Hr Outlook (0000Z Aug 23)… 25% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-32W)

IOH 120 Hr Outlook (0000Z Aug 24)… 25% chance of tropical cyclone formation (eastern tropical Atlantic near 17.5N-37.5W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************

Not in the official outlook


AREA OF INTEREST #24... A tropical wave of low pressure with rotating shower and thunderstorm activity was positioned near 11.5N-57W as of 0000Z. After crossing Lesser Antilles islands over the next 24 hours... this tropical wave has an opportunity to interact with a pair of upper anticyclones with supporting low shear and upper outflow as follows:


(1) The current Caribbean upper vorticity will retorgrade westward and away while pushed around the current Gulf of Mexico upper ridge and later a building central US upper ridge... giving way to an expanding upper anticyclone over the Caribbean. 


(2) The southern vorticity of the current eastern Canada to eastern US upper trough is forecast to retrograde southwestward and away around an upper ridge that later builds over the central US. This will allow for another anticyclone to build in the western Atlantic to the north of Puerto Rico... in between the ongoing western Atlantic upper vortex and the retrograding upper vorticity.


There are multiple possibilities concerning the evolution of this tropical wave over the next five days. The first is that the wave develops further southwest underneath the Caribbean anticyclone. The second is that the northeastern part of the wave takes a more northern track while becoming entangled with area of interest (AOI) #20 and the surface ridge weakness that AOI #20 will be turning north into… potentially allowing the northeastern part of the wave to potentially develop just north of Puerto Rico and underneath the western Atlantic anticyclone. By day 4 my forecast position shown below splits the difference between the northeastern and southwestern solutions. The current model consensus is that the northeastern solution is becoming the most likely… and so by day 5 I forecast a north into the aforementioned surface ridge weakness. I have set odds of tropical cyclone formation to a low 10% as all of the above mentioned influences may simply cause this tropical wave to degenerate into an elongated southwest-northeast surface trough spanning from the central Caribbean to the waters north of Puerto Rico by day 5.


Regardless of tropical cyclone formation or not… this wave will likely produce heavy rainfall and gusty winds across the southern Lesser Antilles within the next 24 hours. By Tuesday and Wednesday this system may produce heavy rainfall over Haiti and the Dominican Republic.

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

IOH 24 Hr Outlook (0000Z Aug 20)... 5% chance of tropical cyclone formation (just west of the southern Lesser Antilles near 12.5N-62W)

IOH 48 Hr Outlook (0000Z Aug 21)... 10% chance of tropical cyclone formation (eastern Caribbean near 13.5N-67W)

IOH 72 Hr Outlook (0000Z Aug 22)... 10% chance of tropical cyclone formation (central Caribbean near 15N-70W)

IOH 96 Hr Outlook (0000Z Aug 23)... 10% chance of tropical cyclone formation (south-southeast of Haiti near 16N-72W)

IOH 120 Hr Outlook (0000Z Aug 24)... 10% chance of tropical cyclone formation (between Haiti and the southeastern Bahamas near 20.2N-72W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************

Formation chance through 48 hours...20%

Formation chance through 7 days (168 hours)...40%


...COMPUTER MODEL SUMMARY... 

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


1200Z (Aug 18) CMC Model Run...

**For area of interest #20... no development shown

**For area of interest #21... tropical wave continues west-northwest as a tropical low and reaches 24N-46.5W at 120 hours

**For area of interest #22... no development shown

**For area of interest #23... tropical wave emerges from western Africa at 30 hours and soon after organizes into a tropical low near 14N-19W at 42 hours... center of tropical low passes over the northern Republic of Cabo Verde Islands at 78 hours... tropical low located near 16.2N-33W at 120 hours

**For area of interest #24... tropical wave organizes into central Caribbean tropical low near 15N-71.5W at 96 hours... subsequently drifts north into Haiti and the Dominican Republic by 114 hours with tropical cyclone formation occuring in the north side of the tropical low and just east of the eastern Bahamas by 126 hours

**Southwest part of area of interest #24 seperates and organizes into a tropical low just offshore of Honduras at 138 hours... while drifting north toward the surface ridge weakness caused by area of interest #24 the tropical low reaches 18.5N-83.8W by 168 hours.


1200Z (Aug 18) ECMWF Model Run...

**For area of interest #20... no development shown

**For area of interest #21... tropical wave continues west-northwest as a broad tropical low whose center reaches 22N-48W by 120 hours.

**For area of interest #22... north side of tropical wave organizes into western Gulf of Mexico tropical low near 25N-95W at 90 hours... tropical low makes landfall just south of the Texas/Mexico border at 108 hours and dissipates inland just south of the border at 120 hours.

**For area of interest #23... tropical wave emerges from western Africa at 24 hours... subsequently organizes into a broad tropical low which passes over the Republic of Cabo Verde Islands at 66 hours... tropical low opens back to a wave near 19.2N-36.2W at 120 hours.

**For area of interest #24... tropical wave by 138 hours degenerates into southwest-northeast tilted surface trough from the Caribbean waters west of Jamaica to the eastern Bahamas... the northeast end of the trough organizes into a tropical low just northeast of the eastern Bahamas by 144 hours.

**Tropical wave emerges from western Africa at 126 hours and undergoes rapid compact tropical cyclone formation just offshore and near 13N-18W at 132 hours... tropical cyclone passes over the southern Republic of Cabo Verde Islands at 162 hours.


1800Z (Aug 18) GFS Model Run...

**For area of interest #20... no development shown

**For area of interest #21... tropical cyclone formation suggested near 18.5N-38.5W at 45 hours... weakens to a remnant low near 19.8N-41.2W at 72 hours... remnant low weakens further to a trough near 23.5N-50W at 120 hours.

**For area of interest #22... north side of tropical wave organizes into western Gulf of Mexico tropical low near 25.2N-95.2W at 93 hours... tropical low makes landfall just south of the Texas/Mexico border at 102 hours and dissipates inland just south of the border at 120 hours.

**For area of interest #23... tropical wave emerges from western Africa at 27 hours... tropical wave organizes into a broad tropical low centered just southeast of the Republic of Cabo Verde Islands at 75 hours... compact tropical cyclone formation suggested within the broad tropical low and near 16N-32.5W at 114 hours... compact tropical cyclone located near 15.5N-35W at 120 hours

**For area of interest #24... tropical wave organizes into a southeastern Caribbean tropical low near 12.5N-63.5W at 42 hours and weakens back to a tropical wave near 66W longitude by 54 hours... wave axis remains stationary through 66 hours while absorbing area of interest #20 to the northeast... north end of the wave axis evolves into a broad tropical low east of the eastern Bahamas at 120 hours.


1200Z (Aug 18) NAVGEM Model Run...

**For area of interest #20... no development shown

**For area of interest #21... tropical cyclone formation suggested near 16N-34W at 12 hours... tropical cyclone continues northwest to 25.8N-45.5W at 120 hours

**For area of interest #22... no development shown

**For area of interest #23... tropical wave emerges from western Africa at 36 hours... tropical wave organizes into a broad tropical low centered just southeast of the Republic of Cabo Verde Islands at 96 hours... tropical low continues west to 15N-26W at 120 hours.

**For area of interest #24... tropical wave evolves into rather large tropical low in the central Caribbean at 96 hours... the tropical low degenerates into a southwest-northeast surface trough spanning from south-southwest of Jamaica to the eastern Bahamas by 126 hours

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