*******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 3 2020 8:02 PM EDT...
See area of interest section below for two disturbances with potential for tropical development over the next day or so. The second area of interest was just added into the National Hurricane Center tropical weather outlook and just after the birdseye view chart above was created...which is why it is marked as not being in the outlook in the chart.
Elsewhere...the CMC and ECMWF models continue to suggest tropical cyclone formation in a few days along or just offshore of the United States southeast coast. A study of GFS model upper-level winds suggests this will now be triggered due to the eastern upper divergence zone of the upper vorticity now located in the Gulf of Mexico (previously located in the northwestn Caribbean)...while the upper vorticity over the central United States plays less of a role while now shown shifting eastward and away in the mid-latitude westerlies...albiet possibly enhancing the eastern upper air outflow in the region. However the GFS itself as well as the NAVGEM do not show tropical cyclone development. Not marking another area of interest for tropical development at this time unless the NAVGEM or GFS joins the CMC-ECMWF consensus...or if observations on satellite imagery later warrant.
AREA OF INTEREST #1...The cut-off upper vortex that was stationary over the northeastern United States has shifted into the northwestern Atlantic as an upper trough diving southward from southeastern Canada has partly eroded the central North America upper ridge that has kept it trapped. In the eastern divergence zone of the upper vortex but also close to the upper vortex center...a new surface frontal low pressure has formed near 37.5N-67.5W and contains a modest amount of shower and thunderstorm activity. Therefore watching to see if it acquires tropical characteristics over the next 24 hours. In my updated outlook below...I have adjusted the forecast track of the surface low southward toward the current ECMWF solution as the surface low has formed further south than I previously anticipated. I have trimmed the odds of subtropical development down to 10% as the National Hurricane Center has not mentioend this disturbance in their tropical weather outlook and the window for subtropical development will dramatically close after 24 hours when the upper vortex becomes absorbed by the upper trough approaching from southeastern Canada...guaranteeing that the surface low pressure will be a definite non-tropical feature along the upper trough's front.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jul 4)...10% chance of subtropical cyclone formation (northwestern Atlantic near 39N-60W)
IOH 48 Hr Outlook (1800Z Jul 5)...0% chance of subtropical cyclone formation (north Atlantic near 44N-45W)
AREA OF INTEREST #2...A re-analysis of satellite imagery and surface observations in the last 24 hours reveals an area of surface rotation developing just offshore of the Carolinas...a surface trough of low pressure...just ahead of the cold front tied to the upper vortex that has moved from the northeastern United States to northwest Atlantic. This disturbance appears to have developed from the eastern divergence zone of the southwestern lobe of the upper vortex as the upper vortex was elongated in nature yesterday...and now has moved southeastward with the cold front to the waters northeast of the Bahamas near 30N-73W while showing some signs of tropical organization...including most recently a circular burst of thunderstorms and southern cirrus outflow clouds streaming into a tiny upper vortex near the eastern Bahamas that is an eastward fracture of an upper vortex that was in the northwestern Caribbean. This tropical disturbance was something that was shown developing in the July 1st cycle of model runs...but not seen in yesterday's runs as the models gave more credence to a broad frontal low pressure that will soon form to the north of this disturbance from a shortwave upper trough to dive southward around the longwave upper trogh from southeastern Canada. Going forward there are mixed signals with the upper-level winds...on the one hand the shortwave upper trough will produce plenty of westerly wind shear north of 30N latitude during the forecast period...on the other hand the small upper vortex near the eastern Bahamas will merge with the southwest fracture of another upper vortex in the central Atlantic...creating a solid upper vortex to the south of the disturbance that will favorably enhance its southern outflow. Given the southern cirrus outflow clouds and growing circular burst of thunderstorms...I give a 30% chance of tropical cyclone formation in the next 24 hours...and I may have to do special updates tonight to increase the odds of development if these trends continue. I am south of the CMC model run regarding track due to current observations of a pure eastward track along 30N latitude at the moment...but a northward angle in track after 24 hours will occur as the disturbance bumps into the west side of the Atlantic subtropical surface ridge. I decrease the odds of development after 24 hours due to cooler waters and increasing placement into the shearing upper westerly winds that the northward angle in track will cause. Interests in Bermuda should monitor the progress of this disturbance as gusty winds and heavy rains...with possible tropical storm conditions...could occur soon in 36 hours (evening of July 4th into the early morning hours of July 5th).
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jul 4)...30% chance of tropical cyclone formation (western Atlantic near 30N-69W)
IOH 48 Hr Outlook (1800Z Jul 5)...15% chance of tropical cyclone formation (east of Bermuda near 32N-61.5W)
IOH 72 Hr Outlook (1800Z Jul 6)...0% chance of tropical cyclone formation (central Atlantic near 35N-55W)
...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 area of interest #1...surface low becomes better defined in the model near 40N-58W in 24 hours...by 48 hours is a non-tropical frontal low pressure southeast of Newfoundland accelerating northeastward into the open north Atlantic. For area of interest #2...possible tropical cyclone formation suggested near 31N-70W in 18 hours...passes just northwest of Bermuda in 36 hours...merges with broad frontal low pressure located to the north by 66 hours and becomes the dominant frontal low pressure center in the area at 39.5N-54W. Elsewhere...possible tropical cyclone formation suggested along the coast of South Carolina by 120 hours...drifting slowly northeastward to the North Carolina coast in the long range.
1200Z ECMWF Model Run...For area of interest #1...surface low becomes better defined in the model near 38N-61.5W in 24 hours...by 48 hours is a non-tropical frontal low pressure south-southeast of Newfoundland accelerating northeastward into the open north Atlantic. For area of interest #2...no tropical cyclone formation shown...has system slide east as a surface trough on the south side of a broad frontal low soon to form to the north...passes just northwest of Bermuda just before 48 hours. Elsewhere...possible tropical cyclone formation suggested just offshore of the North Carolina coast at 144 hours...drifts slowly northward parallel to the US mid-Atlantic coast in the long range.
1200Z GFS Model Run...For area of interest #1...surface low becomes better defined in the model near 39.5N-58W in 18 hours...by 48 hours is a non-tropical frontal low pressure southeast of Newfoundland accelerating northeastward into the open north Atlantic. For area of interest #2...no tropical cyclone formation shown...has system slide east as a surface trough to 31N-70W in 24 hours and lose its identity to broad frontal low pressure to the north shortly after that time. Elsewhere...no tropical cyclone formation shown.
1200Z NAVGEM Model Run...For area of interest #1...surface low becomes better defined in the model near 40.5N-56W in 24 hours...by 48 hours is a non-tropical frontal low pressure southeast of Newfoundland accelerating northeastward into the open north Atlantic. For area of interest #2...has surface trough develop a closed circulation near 32N-70W by 24 hours...has closed ciruclation pass just northwest of Bermuda in 42 hours...loses its identity within broad frontal low pressure area to the north by 72 hours while located near 37N-53.5W. Elsewhere...no tropical cyclone formation shown.
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