*******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.*********
...THURSDAY AUGUST 1 2024 10:09 PM EDT...
As the month of August kicks off... watching two areas of interest for possible tropical cyclone formation as follows:
(1) See area of interest #15 section below on possible northwest Atlantic tropical cyclone formation in the next 24 hours from a mid-level low pressure spin currently in progress
(2) See area of interest #14 section below on increasing likely tropical cyclone formation this weekend in the vicinity of the Florida peninsula or western Cuba from the currently organizing tropical wave of low pressure in the vicinity of Haiti and the Dominican Republic
Elsewhere... another tropical wave of low pressure has seen some increase in rotating thunderstorms near 10N-36W. However in 72 to 96 hours… while it moves into the central tropical Atlantic waters east of the Lesser Antilles… upper winds are forecast to be less favorable for its development as follows… (1) a warm core northwestern Atlantic upper ridge is expected to setup in due to warm southerly flow ahead of the forecast eastern North America surface frontal system... (2) relatively lower pressures between the eastern tropical Atlantic upper ridge and northwestern Atlantic upper ridge will result in suppressing upper vorticity in the central of the tropical Atlantic to the east of the Lesser Antilles ... therefore this wave is not expected to develop.
AREA OF INTEREST #14... The thunderstorm activity of the surface tropical wave of low pressure passing westward across the northern Caribbean Islands has become increasingly well-organized while developing into curved bands that suggest a center of rotation is materializing on the north coast of Hispaniola (Haiti and the Dominican Republic). This system is being helped by an area of reducing shear and upper anticyclonic outflow developing in between an upper vortex near Hispaniola and western Atlantic upper vortex currently near 25N-60W. In the next 24 hours the upper vortex near the southern Lesser Antilles merges with the upper vortex near Hispaniola to make a NW/SE tilted inverted upper trough which begins to retrograde westward toward Central America while pushed by the southern US upper ridge. I previously speculated that the eastern convergence zone of the inverted upper trough may disrupt the surface wave's thunderstorms as the wave moves into the southeastern half of the Bahamas and eastern Cuba. However the recent 1200Z GFS model run suggests divergent anticyclonic flow remaining over the surface wave... and given the already robust field of thunderstorms associated with the wave it seems more reasonable now to assume the latent heat release of the thunderstorms will begin an early weakening of the cool core inverted upper trough to the south to keep the local upper anticyclonic flow going. Thus tropical cyclone formation may already be on the table in the next 24 hours. By 48 hours... as the surface wave continues toward the southern Florida peninsula and western Cuba... the favorable upper anticyclone over the surface wave continues to expand between the weakening inverted upper trough and western Atlantic upper vortex... and combined with the rather warm 30+ deg C waters I begin to sharply raise odds of tropical cyclone formation. Between 48 and 96 hours... a northward turn across the Florida peninsula and into the waters just offshore of the southeastern United States is shown due to the surface ridge weakness of a large eastern North America frontal system to be supported by the upper trough fragments now settling into central North America. Although my current forecast point at 72 hours is over the Florida peninsula... I agree with the NHC's high 70% chance of tropical cyclone formation for that timeframe as the center of whatever circulation develops may be close enough to the rather warm 30+ deg C water surrounding the peninsula to still become a tropical cyclone even if the center is located just inland... and to boot only a small shift in the future forecast track would put the center over water anyway.
For the longer range... beyond day 4... models have come into agreement that this system will miss the northeastward exit with the eastern North America surface frontal system and assoicated upper trough. However a total stall between the conflicting surface ridge building behind the exiting frontal system and Atlantic surface ridge is not currently expected as the models have also trended further south with a shortwave upper trough and associated surface frontal low now expected over the Ohio Valley region of the US in the 4 to 5 day window... thus my outlook below shows a slow northeastward track continuing in the flow ahead of the now-closer surface frontal low for the 96 to 120 hour segment. Regarding odds of tropical cyclone formation for this timeframe... there is no agreement in the models in exactly how a band of upper vorticity to be deposited by the exiting eastern North America frontal upper trough will look like. If it remains an east-west band the upper vorticity would shear this system... however if it ends up as a circular upper vortex over the southeastern US as the recent 1200Z GFS model run suggested upper winds would be more favorable for tropical development thanks to a focused area of upper divergence and lower shear on the southeast side of the vortex. Given the uncertainty in the day 4 to 5 upper wind outlook... I taper down my odds of tropical cyclone formation to 60% for that window of time.
Expect heavy rains and possible gusty winds across Hispaniola (Haiti and the Dominican Republic)... much of the Bahamas... and eastern Cuba for tonight through tomorrow. Interests across western Cuba... the Florida Keys... and Florida peninsula need to carefully monitor this system as tropical cyclone impacts (gusty winds... heavy rains... and coastal surf) are becoming increasingly likely for this weekend and into Monday. Interests across the southeastern United States should also be monitoring this system for early-week tropical cyclone impacts carefully as follows:
(1) should the track veer more west... the panhandle of Florida... southern Georgia...and southeastern Alabama might see tropical cyclone impacts
(2) should the track veer more east... coastal Georgia and the coastal Carolinas would see possible tropical cyclone impacts
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 2)... 15% chance of tropical cyclone formation (north coast of eastern Cuba near 21.2N-76W)
IOH 48 Hr Outlook (1800Z Aug 3)... 50% chance of tropical cyclone formation (north coast of Cuba near 23N-80W)
IOH 72 Hr Outlook (1800Z Aug 4)... 70% chance of tropical cyclone formation (southwestern Florida peninsula but near the coast in vicinity of 26.5N-81W)
IOH 96 Hr Outlook (1800Z Aug 5)... 60% chance of tropical cyclone formation (just offshore of northeastern Florida near 30N-80.5W)
IOH 120 Hr Outlook (1800Z Aug 6)... 60% chance of tropical cyclone formation (offshore of the Georgia/South Carolina border near 31N-79.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT**************************
Formation chance through 48 hours... 40%
Formation chance through 7 days... 70%
AREA OF INTEREST #15... The tail end of the current eastern Canada upper trough now heading toward the Atlantic is diving south from eastern New York while beginning to absorb upper vorticity offshore of North Carolina. Yesterday on satellite pictures a mid-level low pressure spin appeared to materialize offshore of the Carolinas in divergence between northwesterlies flowing into the back side of the offshore upper vorticity and southwesterlies associated with the approaching upper trough which was confirmable by the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=). By 1800Z today the northeastward moving mid-level low pressure spin continued to be confirmed on satellite animation and CIMSS 850 mb vorticity while positioned near 36.5N-70.5W… and as late as 1200Z today the upper air charts suggested the supportive divergence pattern between the offshore upper vorticity and approaching upper trough was continuing. Going forward… once the upper trough finishes absorbing the offshore upper vorticity… the mid-level low pressure spin will become supported by the eastern divergence zone of the upper trough as typically seen with non-tropical systems. However the northeast track of the low pressure spin will keep it along the warm 26 deg C sea surface temp isotherm thru 48 hours… the brisk northeast track of the low pressure spin will mitigate the effect of shear imparted by the upper southwesterly winds… and showers and thunderstorms have notably increased particularly on the southeast half of the low pressure circulation… therefore I have upgraded this system to an area of interest for possible tropical cyclone formation in the next 24 hours and before it becomes overspread by the surface cold front to be driven into the northwest Atlantic by the incoming upper trough. I keep odds of tropical cyclone formation below 50% as it only has a 24-hour window remaining to do so… but have the odds as high as 30% due to the recent increase in the system’s shower and thunderstorm activity.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 2)... 30% chance of tropical cyclone formation (northwestern Atlantic near 39N-61W)
IOH 48 Hr Outlook (1800Z Aug 3)... 0% chance of tropical cyclone formation (north Atlantic near 41N-45W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 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 (Aug 1) CMC Model Run...
**For area of interest #14... evolves into a broad tropical low in the vicinity of western Cuba at 60 hours... begins to curve north into the eastern Gulf of Mexico and becomes a tropical cyclone centered just west of the Florida Keys at 72 hours... the intensifying tropical cyclone makes landfall at the Big Bend region of the Florida panhandle at 102 hours and weakens to an inland tropical storm at the central part of the Georgia/Alabama border through 126 hours... subsequently curves east-northeast across the southeastern United States while interacting with the divergence zone of an incoming shortwave upper trough which causes its transition into a less tropical but still vigorous inland subtropical low whose core reaches the southeastern North Carolina coast by 168 hours
**For area of interest #15... Offshore Mid-level circulation currently positioned east of North Carolina evolves into a surface low near 36N-70W at 24 hours... while paralleing Atlantic Canada coast while on an east-northeast trajectory gradually merges with cold front pushed offshore by current east Canada frontal low through 60 hours... remnant frontal low races east across the open north Atlantic and reaches the waters northeast of the Azores (near 42N-21W) by 126 hours... convergence on east side of building warm core deep-layer ridge to the west dissipates the remnant frontal low near 40.2N-17.5W by 150 hours.
0000Z (Aug 1) ECMWF Model Run...
**For area of interest #14... north side of tropical wave fractures off into a surface trough that turns northwestward toward the north-central Gulf of Mexico by 90 hours... divergence between southwest side of upper vorticity (deposited by eastern North America frontal system/upper trough) and southeast side of southern US upper ridge causes surface trough to evolve into eastward-drifting tropical low that moves into northeastern Gulf of Mexico by 156 hours
**For area of interest #15... Offshore Mid-level circulation currently positioned east of North Carolina moves east-northeast and becomes a short-lived small surface low near 39.5N-60W at 42 hours... soon after the surface low loses identity while absorbed by cold front that pushes offshore from eastern Canada.
1200Z (Aug 1) GFS Model Run...
**For area of interest #14... becomes a tropical depression centered just southwest of Key West Florida at 57 hours... turns north as a strengthening compact tropical cyclone which makes landfall on the northwest coast of the Florida peninsula at 84 hours... under influence of southeast US upper vortex deposited by eastern North America frontal system/upper trough the tropical cyclone is kicked northeastward and re-emerges into the Atlantic from the Georgia coast at 105 hours... combination of eastward push provided by Ohio Valley surface frontal low (produced by shortwave upper trough) and northward pull of ongoing southeastern US upper vortex keeps the tropical cyclone center drifitng northeastward parallel to and just offshore of the South Carolina coast through 132 hours... this motion continues through 168 hours as the frontal low from the Ohio Valley passes just to the north which results in the tropical cyclone center being just offshore of southeastern North Carolina by 168 hours
**For area of interest #15... no development shown
1200Z (Aug 1) NAVGEM Model Run...
**For area of interest #14... north side of tropical wave breaks off into an east-central Gulf of Mexico tropical low offshore of the southwestern Florida peninsula coast by 66 hours... tropical low continues northeastward across the northern Florida peninsula and into the waters just offshore of the southern tip of South Carolina through 96 hours... trpoical low drifts northeastward parallel to the Carolina shore thorugh 132 hours while pinned in weak steering currents between the conflicting Atlantic surface ridge to the east and surface ridge to the north that builds behind exiting eastern North America surface frontal system... while becoming quasi-stationary gradually loses its identity through 168 hours ahead of next surface frontal systems approaching from the Great Lakes region of North America and central US (the weakening through 168 hours likely also due to suppressing overhead cut-off upper vortex that also becomes quasi-stationary after being left behind by the upper trough of the prior eastern North America frontal system).
**For area of interest #15... no development shown
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