BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) 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 via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #97

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


...THURSDAY AUGUST 20 2020 12:35 PM EDT...

See tropical depression thirteen and fourteen sections below for the two currently active and new tropical cyclones in the Atlantic basin. See area of interest section below for the far eastern Atlantic tropical wave of low pressure being monitored for tropical cyclone formation.


Elsewhere...models indicate another vigorous tropical wave worth watching for tropical development could emerge from western Africa in about four days. And also the southern portion of the large upper trough over eastern North America is becoming cut-off in the Gulf of Mexico due to an amplifying upper ridge over western North America. Because tropical depression fourteen appears it now could develop rapidly enough to become strong and tall enough to get pulled toward the eastern side of this upper trough...the potential for another disturbance developing in the eastern Gulf of Mexico under the eastern divergence zone of this cut-off upper trough is very low.


TROPICAL DEPRESSION THIRTEEN...The large sprawling tropical low pressure in the central tropical Atlantic has become tropical depression thirteen overnight...with no strengthening occurring through this morning. Due to the current position of the depression and slightly faster west-northwest forward speed...I have adjusted my forecast points northwestward. For the next 48 hours the current and mainly west forward motion is expected to continue while steered around south side of the Atlantic subtropical surface ridge. After that time...I tilt the track a little more northward while following the forecast countour of the southwestern side of the Atlantic subtropical ridge...which will be increasigly building westward toward the southeasern United States (see tropical depression fourteen section below for more details on the expected evolution of the surface subtropical ridge). This track will take this system across the northeastern Caribbean Islands from the northern Lesser Antilles to the Dominican Republic...then the waters between the Bahamas and Cuba...then toward south Florida and the Florida Keys...over the next five days. The steering situation just after five days could become interesting depending on the evolution of tropical depression fourteen expected to move into the Gulf of Mexico. If fourteen manages to become a hurricane as I currently forecast...this system could perform a fujiwhara type of interaction where it pulls fourteen on a less northward track...and this system in turn gets pulled on a more northward track by fourteen.


Regarding strength...I like the ideas presented by the NAVGEM and CMC where little strengtehning is shown in the next 48 hours...followed by more rapid strengthening after that time. This is because in the short-term this system will be fighting three negative factors...the dry saharan air wrapped around the outer edge of the circulation...central Atlantic upper vorticity getting streteched southwestward toward the eastern Caribbean region by the northwest Atlantic upper ridge which could disrupt the western outflow of this system...and the current large size of the circulation which will need time to consolidate before more rapid strengthening can occurr. After 48 hours...this system will have moved toward a region where the dry saharan air is in less concentration...and the upper vorticity in the eastern Caribbean region will have moved westward and away which will allow the tropical upper ridge axis currently dominating the Atlantic tropics to merge with the northwestern Atalntic upper ridge...providing a vast area of low shear and upper outflow for this system to intensify. I also speculate that this system will have developed a tighter circulation capable of strengthening...especially as it moves toward the mountainous terrain of the Dominican Republic which could help tighten the circulation like we saw when potential tropical cyclone nine consoldiated into Tropical Storm Isaias on July 29 to 30. Thus I show rapid intensification into a hurricane and then a major category 3 hurricane as this system moves past the Dominican Republic...the waters between the Bahamas and Cuba...and toward south Florida and the Florida Keys.


Interests across the northern Lesser Antilles...Virgin Islands...Puerto Rico...the Dominican Republic...Haiti...north coast of Cuba...the eastern and central Bahamas...the southwestern Bahamas in the vicnity of Andros Island...south Florida...and the Florida Keys should begin making preparations for this system. See the bulletins at the home page of this site for potential impacts expected across these land areas over the next five days.

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

0 Hr Position (1200Z Aug 20)...35 mph maximum sustained wind tropical depression centered at 15.4N-50.9W

IOH 24 Hr Forecast (1200Z Aug 21)...40 mph maximum sustained wind tropical storm centered east of the northern Lesser Antilles at 16.5N-57W

IOH 48 Hr Forecast (1200Z Aug 22)...50 mph maximum sustained wind tropical storm centered just southeast of the Virgin Islands and just southwest of the northern Lesser Antilles at 17.5N-63W

IOH 72 Hr Forecast (1200Z Aug 23)...75 mph maximum sustained wind hurricane centered on the north coast of the Dominican Republic at 19.5N-69W

IOH 96 Hr Forecast (1200Z Aug 24)...100 mph maximum sustained wind hurricane centered between Cuba and the Bahamas at 21.5N-76W

IOH 120 Hr Forecast (1200Z Aug 25)...120 mph maximum susateind wind major hurricane centered between the Florida Keys and north of the Cuban coast at 23.5N-82W


AREA OF INTEREST #1 (RECENTLY UPGRADED TO TROPICAL DEPRESSION FOURTEEN)...The tropical wave featuring low pressure spin moving across the central Caribbean Sea has rapidly developed strong thunderstorm bursts and bands overnight...enabling this system to quickly strengthen into the fourteenth tropical depression of this busy 2020 Atlantic Hurricane Season. This system continues to become rapidly organized on satellite pictures...and so I speculate this system will likely be upgraded to a tropical storm later today...perhaps sooner than tropical depression thirteen out in the central tropical Atlantic. This system is slightly north and west of my previous forecast track...and with anticipation for this system to strengthen briskly in the short term my forecast intensity in notably adjusted upward from yesterday and my forecast track is adjusted more northward for the following reasons explained in the next paragraph:


Fourteen will be heavily influenced by the south fracture of the large eastern North America upper trough which is becoming cut-off in the Gulf of Mexico by an amplified western North America upper ridge. The evolution of the western North America upper ridge and also the northwest Atlantic upper ridge (supported by warm air advection ahead of the current front along the United States east coast) will also be big players. Initially the cut-off upper trough's eastern divergence zone is dropping surface pressures along the tail end of the United States east coast front...located in the northern Gulf of Mexico...with this surface low pressure field expectd to bend fourteen's track north enough in the next 24 hours such that it does not make landfall in Nicaragua and Honduras. After 24 hours...the future track of fourteen heavily depends on the strength of this system. This is because the Gulf of Mexico surface low pressure field is expected to weaken as the cut-off upper trough begins to weaken while starved of higher latitude colder air...with the Atlantic surface subtropical ridge instead building westward into the southeastern United States due to the southeastern convergence zone of the northwestern Atlantic upper ridge. The surface ridging over the southeastern United States will strengthen further late in the forecast period as frontal systems over southern Canada driven by shortwave upper troughs will waft the warm air associated with the western North America upper ridge toward the Great Lakes region...with the southeastern convergence zone of the Great Lakes nose of the upper ridge responsbile for strengthening the southeastern United States surface ridge. This means a weaker/shallower system would be steered more westward by the building southeastern United States surface ridge...and a stronger/taller system would be turned more northward by the cut-off upper trough. Given the observations of rapid organization in the previous paragraph...I am now trending toward a stronger/taller system that bends northward in track after 24 hours. The combination of the upper trough's north pull and southeastern United States surface ridge westward push is expected to cause a steady northwestawrd track across the Gulf of Mexico and toward the Texas coast by day 5.


Regarding intensity...I forecast this system to become a strong tropcial storm in the next 24 hours...then show category 1 hurricane strength as this system moves into the northeastern Yucatan peninsula. I do not expect an intensity above category 1 for the Yucatan landfall at this time as the cut-off upper trough may impart some shear or block the western outflow of this system. I show a little weakening to minimal category 1 as this system enters the southern Gulf of Mexico due to ongoing potential shear/western outflow blockage...and also due to the land interaction with the Yucatan. By 96+ hours...the cut-off upper trough will have been pushed westward and away into Texas and northern Mexico by the sprawling western North America to Great Lakes upper ridge...which has potential to reduce the shear and allow additional strengthening. However I do not show intensity above category 2 as the upper trough may still be close enough to dampen the strengthening with some western outflow blockage.


Given this current outlook...I expect peripherial impacts from this system for Jamaica and the Cayman Islands...as well as Belize and northeastern Nicaragua over the next couple of days...with more direct impacts such as heavy rainfall and gusty and potentially damaging winds for northeastern Honduras in 24 hours...and for the eastern and northern Yucatan region of southeastern Mexico and western Cuba in 48 hours. In about 5 days...this system has the potential to strike the Texas coast as a hurricane...and so due to the COVID-19 virus emergency ongoing here I advise interests here to already start gathering storm preparation supplies early as to avoid last minute shopping crowds that could incrase the virus spread. See the bulletins at the home page of this site for more details.

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

0 Hr Position (1200Z Aug 20)...35 mph maximum sustained wind tropical depression centered in the central Caribbean Sea at 16N-79W

IOH 24 Hr Forecast (1200Z Aug 21)...60 mph maximum sustained wind tropical storm centered offshore of the eastern Honduras coast at 17N-85W

IOH 48 Hr Forecast (1200Z Aug 22)...80 mph maximum sustained wind hurricane centered over the northeastern Yucatan peninsula at 20.5N-87W

IOH 72 Hr Forecast (1200Z Aug 23)...75 mph maximum sustained wind hurricane centered over the southern Gulf of Mexico at 22.5N-90W

IOH 96 Hr Forecast (1200Z Aug 24)...95 mph maximum sustained wind hurricane centered in the western Gulf of Mexico at 25N-93W

IOH 120 Hr Forecast (1200Z Aug 25)...105 mph maximum sustained wind hurricane centered offshore of the southern Texas coast at 27.5N-96W


AREA OF INTEREST #2...The vigorous tropical wave of low pressure over western Africa has moved offshore into the eastern tropical Atlantic as of this morning. Initially the tropical wave was producing disorganized thunderstorm activity in its southern half while dry saharan air suppressed its northern half. More recently on colorized infrared satellite the southern thunderstorm activity appears to be becomign slowly organized with some banding features...using these banding features as a clue I assume that the lowest pressure of the tropical wave is currently in the vicinity of 10N-17.5W. This has caused me to nudged my forecast track points a bit southward. Thru the 120 hour forecast period...a steady westward track across the eastern tropical Atlantic under the influence of the steering Atlantic subtropical ridge is expected. This tropical wave will also stay below the axis of tropical upper ridging prevailing across the Atlantic...which will provide a low shear and upper outflow environment conducive to development. Given the current organizational trend...I have raised my peak odds of tropical cyclone formation over the next five days to a medium 50%...not going higher while still being cautious about the dry saharan air covering the north half of this system. For the longer range after the 120-hour forecast period...should this system develop...I am afraid the modeling does not show any mid-latitude frontal systems capable of weakening the steering Atlantic subtropical ridge...and so we may have to deal with another tropical system approaching land areas after tropical depressions thirteen and fourteen...we shall see.

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

IOH 24 Hr Outlook (1200Z Aug 21)...10% chance of tropical cyclone formation (south-southeast of the Republic of Cabo Verde Islands near 11N-22.5W)

IOH 48 Hr Outlook (1200Z Aug 22)...30% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 11.5N-27.5W)

IOH 72 Hr Outlook (1200Z Aug 23)...40% chance of tropical cyclone formation (tropical Atlantic near 12N-32.5W)

IOH 96 Hr Outlook (1200Z Aug 24)...50% chance of tropical cyclone formation (tropical Atlantic near 12.5N-37.5W)

IOH 120 Hr Outlook (1200Z Aug 26)...50% chance of tropical cyclone formation (tropical Atlantic near 13N-42.5W)


...COMPUTER MODEL SUMMARY...

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


0000Z CMC Model Run...For tropical depression thirteen...reaches the northern Lesser Antilles in 48 hours without stregnthening...strengthens to a tropical storm just north of Puerto Rico in 66 hours...rapidly intensifies into a hurricane while moving into the eastern Bahamas in 84 hours...intensifies into an intense hurricane while crossing the Bahamas through 108 hours...makes landfall in southeast Florida as an intense hurricane in 120 hours. For area of interest #1...tropical cyclone formation suggested in the northwestern Caribbean Sea just east of the Belize/Mexico border in 60 hours...weakens to a remnant low pressure while moving across the Yucatan peninsula of southeastern Mexico...emerges into the Bay of Campeche in 84 hours...gradually strengthens back into a tropical cyclone in the Bay of Campeche by 126 hours. For area of interest #2...no tropical cyclone formation shown. Elsewhere...large tropical wave exits western Africa in 102 hours...organizes into a large broad tropical low pressure over the Republic of Cabo Verde Islands in 144 hours.


0000Z ECMWF Model Run...For tropical depression thirteen...weakens to a tropical wave over the northeastern Caribbean Islands in 48 hours. For area of interest #1...tropical cyclone formation suggested in the northwestern Gulf of Mexico near 26.5N-95W in 120 hours. For area of interest #2...no tropical cyclone formation shown. Elsewhere...large tropical wave exits western Africa in 96 hours...organizes into a large broad tropical low pressure over the Republic of Cabo Verde Islands in 144 hours.


0600Z GFS Model Run...For tropical depression thirteen...reaches the northern Lesser Antilles as a strengthening tropical cyclone in 48 hours...passes just north of the Virgin Islands and Puerto Rico as a strong compact tropical cyclone through 60 hours...passes through he Bahamas from 84 through 102 hours as an intense compact tropical cyclone...moves across the southern Florida peninsula as an intense compact tropical cyclone in 120 hours. For area of interest #1...tropical wave organizes into a tropical low pressure in the western Gulf of Mexico in 96 hours near 23N-93W...tropical low pressure moves into the northwestern Gulf of Mexico near 28N-95.5W by 120 hours. For area of interest #2...tropical wave organizes into a compact tropical cyclone just offshore of western Africa near 21.5N-18.5W in 36 hours...reaches the southern Republic of Cabo Verde Islands in 60 hours while weakening...weakens further to a tropical wave near 35W longitude in 102 hours.


0600Z NAVGEM Model Run...For tropical depression thirteen...no strengthening shown till system passes just north of the Lesser Antilles and Virgin Islands in 42 hours...passes just north of Puerto Rico in 54 hours with additional strengthening...moves across the Bahamas from 78 through 102 hours while becoming an intense tropical cyclone...moves into south Florida as an intensse tropical cyclone in 120 hours. For area of interest #1...tropical cyclone formation suggested on the northeast coast of the Yucatan peninsula in 84 hours...begins to rapidly intensify in the western Gulf of Mexico near 25N-92.5W in 126 hours. For area of interest #2...no tropical cyclone formation shown. Elsewhere...large tropical wave exits western Africa in 102 hours...organizes into a large broad tropical low pressure that covers the Republic of Cabo Verde Islands and the waters southwest of the islands in 144 hours.

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