MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #49
*******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.**********
...WENDESDAY JULY 1 2020 11:20 PM EDT...
See area of interest sections below for western Atlantic disturbances being generated by the cut-off upper vortex over the northeastern United States that are being monitored for possible tropical development. Elsewhere...computer model runs have trended in showing yet another surface low pressure forming in the western Atlantic between the Carolinas and Bermuda in a couple of days...to be initiated by split flow upper divergence between the upper vortex and upper riding in the western Atlantic. As suggested by the 1200Z ECMWF model run from earlier today...upper-level winds for this feature could become more favorable for tropical development as wind shear drops when the upper vortex lifts northeastward and away while absorbed by an upper trough diving southward from southeastern Canada. Given that this is a new feature that was not shown in models in previous days...will wait to see if models are consistent before declaring yet another area of interest for tropical development.
And finally...the GFS model continues to suggest another subtropical or tropical disturbance emerging offshore of the Carolinas in a few days with the support of the upper vortex that has recently moved into the southeastern United States. However waiting for support from the additional computer modeling systems before considering this feature an area of interest for tropical development.
AREA OF INTEREST #1...The western Atlantic surface low pressure spin that formed near 32N-72W yesterday under the support of outflow underneath the western Atalntic upper ridging is now accelerating north-northeastward on the west side of the Atlantic surface subtropical ridge and is now passing the waters north of Bermuda. The thunderstorm activity has become streteched north to south in the eastern semircircle of the circulation as the cold front being driven by the northeastern United States upper vortex has overran the circulation and made it transition to a non-tropical low pressure along the front that is now supported by the eastern divergence zone of the upper vortex. Given that this surface low pressure is moving rapidly northeastward toward cooler waters...it is expected to stay as a non-tropical feature...possibly getting additional support from the divergence zone of a high-latitude upper trough approaching from southeastern Canada as it rides along the front. Therefore is my final statement on this low pressure system on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jul 2)...0% chance of tropical cyclone formation (just south of Newfoundland near 45N-53W)
AREA OF INTEREST #2...Yesterday...there had been some indication in the model runs that the cut-off upper vortex that has been persisting over the northeastern United States would shift eastward toward area of interest #1 and energize the area of interest with its eastern divergence zone. Based on today's computer model runs and current observations that area of interest #1 is moving rapidly northeastward and will not have a chance to interact with the upper vortex...it now appears more likely the upper vortex will generate a seperate low pressure area in the vicinity of 40N-60W in about 3 days. Although the water temperatures at this location barely support tropical activity...the cold temperatures of the upper vortex may aid in instability such that the surface low pressure may acquire tropical characteristics. Therefore I have marked the upper vortex itself as a new area of interest for tropical development...giving it a modest 30% odds of subtropical development at 72 hours due to the unamimous model support showing a well-defined surface low pressure forming. I do not have higher odds at this time as I have some uncertainty if a front driven by the upper trough diving southward from southeatern Canada will keep this system non-tropical. By 96 hours this upper trough is expected to absorb the upper vortex...which will increase wind shear and propel this system east-northeastward into cooler waters...factors which dramatically reduce the potential for tropical development...therefore I have 0% odds of development by that timeframe.
IOH 24 Hr Outlook (1800Z Jul 2)...0% chance of subtropical cyclone formation (south of Massachusetts near 39N-71W)
IOH 48 Hr Outlook (1800Z Jul 3)...10% chance of subtropical cyclone formation (northwestern Atlantic near 38N-65W)
IOH 72 Hr Outlook (1800Z Jul 4)...30% chance of subtropical cyclone formation (northwestern Atlantic near 40N-60W)
IOH 96 Hr Outlook (1800Z Jul 5)...0% chance of subtropical cyclone formation (east-southeast of Newfoundland near 44N-50W
...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...low pressure reaches peak strength at 40.5N-65W in 18 hours then loses defintion at 42.5N-60W in 24 hours. Elsewhere...northeastern US upper vortex generates possible tropical or subtropical cyclone near 40N-55W at 78 hours (area of interest #2) and also another broad surface low pressure offshore of the Carolinas by 48 hours that drifts eastward toward Bermuda by 96 hours.
1200Z ECMWF Model Run...For area of interest #1...low pressure reaches 42N-60W in 24 hours...drifts east-southeastward to 41N-54W by 72 hours...then accelerates east-northeastward into the open north Atlantic as a non-tropical frontal low by 96 to 120 hours. Elsewhere...northeastern US upper vortex generates broad surface low pressure offshore of the Carolinas by 48 hours that drifts eastward toward Bermuda by 96 hours while possibly a tropical cyclone.
1800Z GFS Model Run...For area of interest #1...surface low pressure loses defintion just south of Newfoundland by 24 hours. Elsewhere...northeastern US upper vortex generates possible tropical or subtropical cyclone near 40N-60W at 66 hours (area of interest #2) and also another broad surface low pressure offshore of the Carolinas by 48 hours that drifts eastward toward Bermuda by 96 hours. Yet another surface low pressure shown forming offshore of the Carolinas by 108 hours in response to eastern divergence zone of cut-off upper vortex over the southeastern United States.
1800Z NAVGEM Model Run...For area of interest #1...surface low pressure loses defintion just south of Newfoundland by 24 hours. Elsewhere...northeastern US upper vortex generates broad surface low near 40N-62W at 66 hours (area of interest #2) and another broad surface low pressure offshore of the Carolinas by 42 hours that drifts eastward toward 32.5N-70W by 108 hours.