MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #37
*******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 JUNE 19 2020 6:39 PM EDT...
See area of interest sections below for the potential of tropical cyclone development in the northwest Atlantic in the coming days. Elsewhere...the GFS and ECMWF runs described in the computer model summary below show a surface low pressure spin forming in the open central Atlantic by the timeframe that is now 48 hours away in response to a string of upper vorticity that originated from the eastern United States...and is now currently expected to dive south and become a cut-off upper vortex in the central Atlantic in response to the upper ridge currently building in the western Atlantic. However not considering this feature as an area of interest for tropical development as the forecast location of this disturbance is over waters just below the 26 deg C threshold for tropical development...with the forecast upper vortex also being too warm to aid in tropical development at those water temperatures.
And finally...the configuration of the Madden Julian Oscillation (MJO) favorble for tropical cyclone activity appears to be shifting eastward toward the eastern Pacific and western Atlantic regions (https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml). Computer models by next week also show a large upper ridge building over the eastern Pacific and western Gulf of Mexico region which would favor tropical development...but at this time the NAVGEM...GFS...and CMC favor tropical development on the eastern Pacific side instead of the western Gulf of Mexico.
AREA OF INTEREST #1...The southeastern divergence zone of a cut-off upper vortex over the eastern United States is supporting showers and thunderstorms located offshore of the southeastern United States coast. Watching to see if this activity later becomes a tropical cyclone while shifting northeastward into the northwestern Atlantic where the zone of upper divergence will continue as the upper vortex itself also moves into the northwest Atlantic. Tropical cyclone development may also occurr with the support of anticyclonic outflow beneath western Atlantic upper ridging being generated by the warm southerly surface flow on the west side of the Atlantic surface subtropical ridge. Vertical wind shear values unfavorable to tropical development will be on the lower side due to the circular shape of the upper vortex as it moves into the northwest Atlantic...and due to the amplified nature of the western Atlantic upper ridging to be located just east of the upper vortex. However I keep odds of tropical cyclone development at 0% for the next 24 hours as there are no current signs of organization in the thunderstorm activity. By 48 hours...I raise odds of development to 15% as the forecast takes this system over a warm swath of Gulf Stream waters. I have not raised odds of development above 15% as the computer models either show a weak surface low...or alternatively a stronger surface low but located further to the northeast and over cooler waters. The GFS in the longer range conitnues showing the upper vortex being cut-off from the jet stream for longer...thus moving more slowly eastward...as it shows the current warm upper ridging over southeastern Canada to the north being stronger...of course whether that materializes or not depends on exactly how much warm air advection occurs out ahead of the slow-moving central United States frontal system. However the GFS also still shows the surface low escaping the upper vortex and accelerating northeastward in the surface southwesterly flow on the northwest side of the Atlantic subtropical ridge...with the CMC and ECMWF joining this idea...only the NAVGEM now shows the surface low staying entangled with the upper vortex on a slow and more easward drift. So due to the majority model opinion at the present...I have adjusted my 72 and 96 hour forecast points more northeastward and over cooler waters...thus this is when I also taper off odds of development back toward 0%. On a final note...this system by 72 and 96 hours may resemble a more subtropical system should it indeed stay entangled with the upper vortex as the NAVGEM still shows.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 20)...0% chance of tropical cyclone formation (northwestern Atlantic near 35N-70W)
IOH 48 Hr Outlook (1800Z Jun 21)...15% chance of tropical cyclone formation(northwestern Atlantic near 38N-66W)
IOH 72 Hr Outlook (1800Z Jun 22)...10% chance of tropical cyclone formation (northwestern Atlantic near 40N-62W)
IOH 96 Hr Outlook (1800Z Jun 23)...0% chance of tropical cyclone formation (northwestern Atlantic near 41N-59W)
...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 pressure shown forming in the northwest Atlantic near 39N-65W at 66 hours...drifts northeastward to 42N-57.5W by 120 hours while at mature strength.
1200Z ECMWF Model Run...For area of interest #1...no tropical cyclone formation shown...but a weak surface low shown to form in the northwestern Atlantic near 40N-66W...shifting northeast and dissipating southeast of Nova Scotia by 120 hours. Elsewhere...defined surface low pressure spin shown developing in the open central Atlantic near 30N-48W from 48 to 72 hours.
1200Z GFS Model Run...For area of interest #1...weak surface low pressure area shown to form north-northwest of Bermuda near 35.5N-65.5W at 48 hours which then moves into the northwest Atlantic southeast of Nova Scotia where it reaches peak strength near 43N-61W...weakens to a surface trough at a location south-southwest of Newfoundland by 102 hours. Elsewhere...weak surface low pressure spin shown developing in the open central Atlantic near 30N-48W at 36 hours...dissipates by 102 hours.
1200Z NAVGEM Model Run...For area of interest #1...surface low pressure shown forming in the northwest Atlantic near 39N-67W at 54 hours...drifts east-northeastward and dissipates near 41N-59W by 126 hours.