*******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 JULY 30 2020 11:45 PM EDT...
See Tropical Storm Isaias section below for the only active tropical cyclone in the Atlantic basin. See area of interest section below for a far eastern tropical Atlantic tropical wave east-southeast of the Republic of Cabo Verde Islands that has developed a low pressure spin over the last 24 hours. Elsewhere...the tropical wave currently passing 41W is currently inactive due to ingestion of dry Saharan air...but its north side is expected to reach the waters between the Caribbean Islands and Bermuda in about three days where it could interact with the eastern divergence zone of an upper vortex to consolidate from the current axis of upper vorticity in the central Atlantic...which could result in the formation of a tropical disturbance according to the NAVGEM...GFS...and CMC model runs. If these model trends continue...will upgrade this tropical wave to another area of interest for tropical development.
Updated image of Tropical Storm Isaias as the above birdseye view chart is a few hours old.
TROPICAL STORM ISAIAS...The large tropical wave of low pressure that was roaming the eastern Caribbean Sea has undergone substantial changes and has become much better organized into a now strong tropical storm Isaias over the last 24 to 36 hours. The wave was previously disorganized while stretched north to south...but it seems the push toward the Dominican Republic mountainous terrain provided convergence that allowed the north side of the stretched circulation to consolidate...significantly become better organized along the north Dominican Republic coast...and strengthen. The more north position of Isaias has shifted the forecast track points notably to the north and east...and the strengthening troipcal storm is poised to track through the Bahamas and then near or along much of the United States east coast during the 120-hour forecast period.
An axis of upper vorticity spanning the central and western Atlantic basin is likely to continue pulling Isaias system on a northward angle as Isaias is now tall enough to be guided by upper level winds...thus a northward angle in track is shown throughout the forecast period. My initial northward angle is less than the 1800Z GFS as Isaias has a history of tremendous thunderstorm bursts...which I believe will release enough latent heat to weaken the cool core upper vorticity. The northward angle in track likely to increase after 48 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. Regarding intensity...I forecast strengthening to a category 2 hurricane over the next 48 hours as I believe Isaias will be able to mitigate shear from the upper vorticity and the upper trough to approach from the central United States by producing enough thunderstorm latent heat to keep an anticyclone over the storm...I do not expect anything above that intensity at this time however as the western outflow of the storm will likely struggle against the upper vorticity. Weakening is shown after 48 hours as the large approaching upper trough will likely overwhelm Isaias with southwesterly shear regardless of how much latent heat release is being generated. However the weakening rate is shown to be slow as divergence on the east side of the upper trough could support Isaias...perhaps making it transition to a powerful non-tropical remnant gale as it track near or along the northeastern United States coast by Tuesday.
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 Carolina coast to prepare for possible strong hurricane conditions to avoid a last minute crowded rush to get supplies that increases the potential of the virus spread. 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 (0000Z Jul 31)...60 mph maximum sustained wind tropical storm centered on the north Dominican Republic coast at 19.9N-71.2W
IOH 24 Hr Forecast (0000Z Aug 1)...95 mph maximum sustained wind hurricane centered just south of the central Bahamas at 22.5N-76W
IOH 48 Hr Forecast (0000Z Aug 2)...105 mph maximum sustained wind hurricane centered just nortwest of Andros Island and southwest of Grand Bahama Island at 26N-78.8W
IOH 72 Hr Forecast (0000Z Aug 3)...95 mph maximum sustained wind hurricane centered offshore of northeastern Florida at 29.5N-79.5W
IOH 96 Hr Forecast (0000Z Aug 4)...85 mph maximum sustained wind hurricane centered on the North Carolina coast between Cape Fear and Cape Hatteras at 34.5N-78W
IOH 120 Hr Forecast (0000 Aug 5)...75 mph maximum sustained wind hurricane transitioning to non-tropical frontal gale over Rhode Island at at 41.5N-72W
Updated image of area of interest #1 as the above birdseye view chart is a few hours old.
AREA OF INTEREST #1...A tropical wave in the far eastern Atalntic to the east-southeast of the Republic of Cabo Verde has spun up a well-defined center of low pressure over the last 24 hours...and is currently located at 14.5N-20.5W. This system is taking an unusual northward drift at this location...usually the Atlantic subtropical surface ridge keeps tropical waves 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. Model guidance has been spotty over the last 24 hours...with this system occasionally showing up in different models and forecast to have a straight north drift for 24 more hours. Thus my forecast position at 24 hours is due north of the current position...followed by a more west angle in track by 48 hours 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 by 48 hours upon which time I drop odds of development to 0%. Meanwhile I have odds of development at a low 25% for the next 24 hours as this disturbance already has lost thunderstorm activity on its north side...likely from the dry saharan air layer.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Aug 1)...25% chance of tropical cyclone formation (east of the Republic of Cabo Verde Islands near 16N-20.5W)
IOH 48 Hr Outlook (0000Z Aug 2)...0% chance of tropical cyclone formation (north-northeast of the Republic of Cabo Verde Islands near 17.5N-22W)
...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 Tropical Storm Isaias...located between eastern Cuba and the Bahamas at 24 hours as a tropical storm...located between the western Bahamas and southeast Florida in 48 hours as a tropical storm...makes landfall at the south tip of Florida in 60 hours...while moving northward along the west coast of the Florida peninsula weakens to a remnant low in 90 hours. For area of interest #1...no tropical cyclone formation shown. Elsewhere...north end of broad tropical wave of low pressure currently at 41W longitude fractures into a seperate surface trough of low pressure in the western Atlantic near 24N-68W in 108 hours...develops into surface low pressure center near 28N-71W in 126 hours.
1200Z ECMWF Model Run...For Tropical Storm Isaias...reaches hurricane force between eastern Cuba and the Bahamas in 24 hours...curves northwestward into the western Bahamas as a possibly intense hurricane in 48 hours...reaches the east-central coast of Florida as a possibly intense hurricane in 72 hours...curves northward and makes landfall just west of Cape Fear North Carolina in 120 hours as a possibly intense hurricane. For area of interest #1...no tropical cyclone formation shown.
1800Z GFS Model Run...For Tropical Storm Isaias...reaches hurricane force while moving west-northwest into the central Bahamas in 24 hours...reaches the western Bahamas as a possibly intense hurricane in 36 to 48 hours...curves northward from the western Bahamas and makes landfall near Cape Fear North Carolina as a possibly intnse hurricane in 90 hours. For area of interest #1...weak low pressure area shown moving northward to the east of the Republic of Cabo Verde Islands through 30 hours...dissipates shortly thereafter. Elsewhere...north end of broad tropical wave of low pressure currently at 41W longitude produces a surface low pressure near 23N-62W in 84 hours...possibly develops into a tropical cyclone while moving west-northwest and reaching the western Atlantic near 27.5N-69W in 120 hours.
1200Z NAVGEM Model Run...For Tropical Storm Isaias...located between eastern Cuba and the Bahamas at 24 hours as a tropical storm...reaches western Bahamas as a stronger tropical storm in 48 hours...reaches hurricane strength just east of Florida in 72 hours...crosses the North Carolina Outer Banks as a possibly intense hurricane in 108 hours...located just east of New Jersey in 120 hours. For area of interest #1...no tropical cyclone formation shown. Elsewhere...north end of broad tropical wave of low pressure currently at 41W longitude produces a surface low pressure just north of the Lesser Antilles near 19N-62.5W in 90 hours...located at 26.5N-68W at 126 hours.