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 #77

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


...FRIDAY JULY 31 2020 5:44 PM EDT...

See Hurricane Isaias and tropical depression ten sections below for all active tropical cyclones in the Atlantic basin. See area of interest section below for the central Atlantic tropical wave of low pressure being monitored for development.

Updated image of Hurricane Isaias as the above birdseye view chart is a few hours old.


HURRICANE ISAIAS...Isaias strengthened into an 80 mph maximum sustained wind hurricane late last night...but as of this morning and early afternoon has weakened slightly to 75 mph while encountering some westerly shear from an axis of upper vorticity that has been spanning the central to western Atlantic basin. The hurricane has passed through the eastern Bahamas...and is poised to affect the central and western Bahamas through the next 24 hours.


The axis of upper vorticity is expected to continue pulling Isaias on a northward angle as Isaias is tall enough to be guided by upper level winds...thus a northward angle in track is shown throughout the forecast period. I have made no changes to my short-term forecast track as Isaias is on par with it so far. The northward angle in track likely to increase after 24 hours as the frontal system across the eastern United States creates a break in the Atlantic surface subtropical ridge...and as the upper trough over the central United States nears and also drags Isaias with plenty of upper southwestery flow. I have adjusted the later part of my forecast track slightly westward and closer to land as the models have trended with a more amplified upper trough...which will make the upper steering flow more southerly. Regarding intensity...I have lowered the intensity forecast overall as Isaias has not been able to fight off the shear as effectively while having smaller sized thunderstorm bursts instead of larger ones that would otherwise weaken the upper vorticity with latent heat release. Thus my forecast peak now calls for a top end category 1 hurricane for the western Bahamas instead of a category 2. Weakening is shown after 24 hours as the large approaching upper trough will likely overspread Isaias with stronger southwesterly shear. However the weakening rate is shown to be slower as the models have trended with a more amplified approaching upper trough which would keep wind shear lower. In addition the eastern divergence zone of the upper trough will likely support Isaias by making it transition to a powerful non-tropical remnant gale as it track near or along the northeastern United States coast by Tuesday...and across New Brunswick...Nova Scotia...and Prince Edward Island by Wednesday.


See bulletins at the home page of this site for impacts regarding the Bahamas and United States east coast. It is concerning that Isaias will be passing over or near the western Bahamas islands devastated and still recovering from Hurricane Dorian from September of last year. Due to the COVID-19 virus emergency ongoing across the southern United States...I suggest now is the time from the Florida east coast to coastal South Carolina and eastern North Carolina...as well as southeastern Virginia...to prepare for possible hurricane conditions to avoid a last minute crowded rush to get supplies that increases the potential of the virus spread. If you must retreive supplies in a crowded setting...wearing a mask and frequent hand sanitizing will reduce your risk of contracting COVID-19. Also I would suggest thinking about the use of a family/friend residence or hotel location further inland if you live in an area prone to coastal storm surge in case you may have to relocate as the storm approaches and details of exact impacts become clearer...as a public shelter may not be as ideal for controlling your exposure to COVID-19. While the current forecast track would prevent hurricane conditions from northeast Florida to the southern South Carolina coast...coastal storm surge is still a possibility...and a west shift in the track would require a last minute preparation for hurricane conditions and drive crowds...so preparing early even on this segment of the coast to avoid crowds amid the COVID-19 pandemic would be a good idea just in case.

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

0 Hr Position (1800Z Jul 31)...75 mph maximum sustained wind hurricane centered just south of the central Bahamas at 22.2N-75.2W

IOH 24 Hr Forecast (1800Z Aug 1)...95 mph maximum sustained wind hurricane centered on the northwest coast of Andros Island in the western Bahamas at 25N-78.5W

IOH 48 Hr Forecast (1800Z Aug 2)...85 mph maximum sustained wind hurricane centered offshore of northeastern Florida at 29N-79.5W

IOH 72 Hr Forecast (1800Z Aug 3)...80 mph maximum sustained wind hurricane centered on the North Carolina coast at Cape Fear at 34N-78W

IOH 96 Hr Forecast (1800 Aug 4)...70 mph maximum sustained wind tropical storm centered over western Long Island New York at 40.8N-73.8W

IOH 120 Hr Forecast (1800Z Aug 5)...Gale force remnant frontal cyclone centered over the Gulf of Saint Lawrence at 47N-63.5W

Updated image of area of interest #1 (recently upgraded to Tropical Depression Ten) as the above birdseye view chart is a few hours old.


AREA OF INTEREST #1 (RECENTLY UPGRADED TO TROPICAL DEPRESSION TEN)...A tropical wave in the far eastern Atlantic has left behind a well-defined spin of low pressure at a location to the east-southeast of the Republic of Cabo Verde Islands. A small but well-organized thunderstorm burst has persisted directly over the center of spin today...and the National Hurricane Center has recently upgraded this feature to tropical depression ten. The depression is taking an unusual northward drift at its current location...usually the Atlantic subtropical surface ridge keeps disturbances moving westward in this region! My answer for this is that a northeastern Atlantic frontal cyclone has weakened the ridge...perhaps just enough to coax this system toward an African monsoonal surface low pressure field to the northeast over Mauritania. My forecast track points are nudged southeast based on the current position of the depression...but is based on the philosophy that this system will gradually curve more westward while passing east and then northeast of the Republic of Cabo Verde Islands as the Atlantic subtropical ridge rebuilds when the frontal cyclone moves away. On this track...this system will reach water temps below 26 deg C just after 24 hours upon which time I forecast dissipation to a remnant low. In addition I expect dissipation due to the dry saharan air layer looming to the north. The intensity forecast is a bit uncertain...while I do call for no additional strengthening due to the unfavorable aforementioned thermodynamic conditions...on the other hand this system remains below favorable tropical upper ridging with low shear and upper outflow...so I wouldn't be entirely suprised at this point if the depression becomes a tropical storm before eventually weakening.

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

0 Hr Position (1800Z Jul 31)...35 mph maximum sustained wind tropical depression centerd east-southeast of the Republic of Cabo Verde Islands at 15N-20W

IOH 24 Hr Forecast (1800Z Aug 1)...35 mph maximum sustained wind tropical depression centered northeast of the Republic of Cabo Verde Islands at 17N-21W

IOH 48 Hr Forecast (1800Z Aug 2)...Remnant low centered north-northeast of the Republic of Cabo Verde Islands at 19N-23W


AREA OF INTEREST #2...A broad tropical wave of low pressure in the central Atlantic has been largely inactive due to ingestion of dry saharan air...but various model runs have insisted that the north end of the wave will organize into a tropical disturbance to be supported by the eastern divergence zone of an upper vortex to consolidate from the current axis of upper vorticity in the cenral Atlantic. The National Hurricane Center as a result has introduced this tropical wave into their tropical weather outlook. The north end of the tropical wave is already beginning to show signs of activity in the vicinity of 15N-48W even before interacting with the forecast upper vortex. Through the middle part of the forecast period...the warm upper ridge in the western Atlantic is expected to push the upper vortex westward and away and overspread this disturance...which will keep upper winds quiet favorable for development by keeping wind shear low and upper outflow high. Thus I have a peak medium 40% odds of development...not going high with odds of development as of now as the computer model support is on the weak side and as this system is not yet organized. By the end of the forecast period...I nudge odds of development downward as the upper trough forecast to recurve Hurricane Isaias north and northeast merges with the forecast upper vortex while keeping the vortex pushed toward the disturbance...which will begin to increase some wind shear. Forecast track of this disturbance is straighfoward...a west-northwest to northwest trajectory around the southwest side of the Atlantic surface subtropical ridge.

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

IOH 24 Hr Outlook (1800Z Aug 1)...5% chance of tropical cyclone formation (tropical Atlatnic near 16N-53W)

IOH 48 Hr Outlook (1800Z Aug 2)...15% chance of tropical cyclone formation (just northeast of the Lesser Antiles near 18N-58W)

IOH 72 Hr Outlook (1800Z Aug 3)...30% chance of tropical cyclone formation (western Atlantic near 21N-64W)

IOH 96 Hr Outlook (1800Z Aug 4)...40% chance of tropical cyclone formation (western Atlatnic near 24N-68W)

IOH 120 Hr Outlook (1800Z Aug 5)...35% chance of tropical cyclone formation (western Atlantic near near 27N-72W)


...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 Hurricane Isaias...shown to make landfall on the southeast Florida coast in 30 hours...weakens to a tropical storm on the southwest Florida peninsula cost through 54 hours...weakens to a remnant low jusat north of Tampa Bay Florida in 78 hours. For area of interest #1...loses its identity just northeast of the Republic of Cabo Verde just after 18 hours. For area of interest #2...north end of broad tropical wave of low pressure fractures into a seperate surface trough of low pressure in the western Atlantic near 24N-66W in 78 hours...develops into surface low pressure center near 27N-69W in 96 hours...surface low located west of Bermuda near 31.5N-69W in 126 hours.


0000Z ECMWF Model Run...For Hurricane Isaias...reaches the central Bahamas as a possibly intense hurricane in 24 hours...located just offshore of east-central Florida in 72 hours...moves north-northeast across the Outer Banks of North Carolina in 120 hours. For area of interest #1...drifts northward to the east of the Republic of Cabo Verde Islands and loses its identity just after 24 hours. For area of interest #2...no tropical cyclone formation shown.


1200Z GFS Model Run...For Hurricane Isaias...reaches the western Bahamas as a possibly intense hurricane in 24 hours...makes landfall at this intensity over southeast Florida in 42 hours...continues northward along the east-central and northeast Florida coast through 60 hours while wekening...re-strengthens just offshore of Georgia and South Carolina and re-strengthens while making landfall on the North Carolina/South Carolina border in 78 hours...moves across Virginia and US mid-Atlantic coast through 90 hours...makes landfall on Long Island New York in 96 hours...moves over Cape Cod Massachusetts in 102 hours...weakens while curving eastward across Nova Scotia in 120 hours. For area of interest #1...drifts northward to the east of the Republic of Cabo Verde Islands and loses its identity just after 12 hours. For area of interest #2...north end of broad tropical wave of low pressure fractures into a seperate surface trough north of the Lesser Anilles near 21N-61W in 66 hours...develops into a surface low west-near 26N-70W in 120 hours.


0600Z NAVGEM Model Run...For Hurricane Isaias...makes landfall in southern Florida in 48 hours...moves northward along Florida peninsula west coast through 78 hours...shifts northeast into northern Florida in 84 hours...continues northeastward along Georgia coast through 96 hours...makes landfall on South Carolina coast in 102 hours...continues northeastward across central North Carolina in 108 hours...southeast Virginia in 114 hours...continues northeastward across Maryland and into southeastern Pennsylvania in 120 hours. For areas of interest #1 and #2...no tropical cyclone formation shown.

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