MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #194
*******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.**********
...SUNDAY NOVEMBER 29 2020 5:48 PM EDT...
See area of interest section below for the northeast Atlantic deep layered low pressure near the Canary Islands being monitored for tropical development. Elsewhere...the south end of the current upper trough over the northwest Atlantic will become cut-off into a central Atlantic vortex by a warm deep-layered ridge to form in the warm sector of a forecast strong eastern US frontal cyclone...which could produce yet another subtropical disturbance in the open central Atlantic. So far the model consensus shows a subtropical surface low that stays north of warm 26 deg C waters and the upper vortex (forecast to measure around 1205 dekameters in height at 200 mb) will likely not be cold enough to aid in generating strong enough thunderstorm activity for subtropical cyclone formation. Therefore have not added
another area of interest in the central Atlantic.
And finally the upper-level anticyclonic center of the deep-layered ridge to form in the warm sector of the forecast eastern US frontal cyclone is expected to settle over the southern Caribbean Sea where it could enhance the upper outflow and thunderstorms in the region. The southwesterly flow ahead of the frontal cyclone’s upper trough may also enhance the poleward upper outflow in the region as well. The GFS model run continues to suggests possible tropical development in the southern Caribbean over the next few days. However the GFS has a recent history of incorrectly forecasting tropical development in this region nearly two weeks ago...therefore not adding a new area of interest in the southern Caribbean at the present time.
AREA OF INTEREST #1...Continuing to monitor a northeastern Atlantic deep-layered low pressure system...consisting of an upper vortex and surface cyclone...for acquisition of tropical characteristics. Even though water temps in the region are currently running at 20 deg C...the upper vortex (measuring at 1160 dekameters in height at 200 mb) has been plenty cold enough to raise instability at these water temps...and as a result organizing bands of showers and thunderstorms have been persistent around the surface cyclone center. Therefore I have raised short term odds of subtropical cyclone formation to a high 70%. I have also nudged the short-term track forecast track points westward due to the current position of the surface cyclone...but because the surface cyclone is currently beneath the southwest quadrant of the upper vortex the vortex is forecast by models to pull the surface cyclone eastward closer to Madeira Island in the next 24 hours. Therefore expect an increase in gusty winds at the island over the next hours.
After the deep-layer ridge currently to the northwest moves into Europe...in the longer term there will be two competing mechanisms that could move this system away from Madeira Island. One is the approach of the current northwestern Atlantic upper trough which would push this system east...and the other is another deep-layered ridge to form to the west in the warm sector of a strong frontal cyclone to eject from the eastern US which would push this system to the southwest. The model runs for a second day in a row have leaned toward a southwest drift in the forecast track of the surface cyclone and upper vortex...and my updated forecast track below in the long term is a bit faster to the southwest to reflect increased confidence in this solution. This would mean an end to gusty winds on Madeira Island by Tuesday. In the long range and when the southwest drift of this system commenced...I taper the odds of development downward as the surface cyclone (if it fails to develop a tropical thunderstorm core with mid-level warm core upper outflow) will begin to weaken beneath the center of the upper vortex where there is a lack of divergence as we see with typical post-mature mid-latitude storms. In addition while remaining cut-off from high latitude cold air...the cold core upper vortex will increasingly weaken and warm to stabilizing temps (measure towards 1200+ dekameters in height at 200 mb) by 96+ hours...which would put an end to any tropical development especially as the southwest track will not go south enough to the needed warm 26 deg C waters to otherwise sustain tropical development. Thus the odds of tropical development are dropped to 0% by 120 hours.
IOH 24 Hr Outlook (1800Z Nov 30)...70% chance of subtropical cyclone formation (just northwest of Madeira Island near 34.5N-18W)
IOH 48 Hr Outlook (1800Z Dec 1)...50% chance of subtropical cyclone formation (eastern Atlantic near 34.5N-20W)
IOH 72 Hr Outlook (1800Z Dec 2)...30% chance of subtropical cyclone formation (eastern Atlantic near 33N-21.5W)
IOH 96 Hr Outlook (1800Z Dec 2)...10% chance of subtropical cyclone formation (eastern Atlantic near 30N-22.5W)
IOH 120 Hr Outlook (1800Z Dec 2)...0% chance of subtropical cyclone formation (eastern Atlantic near 25N-22.5W)
...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...center of surface cyclone stalls just northwest of Madeira Island from 12 to 36 hours...afterwards drifts southwest while weakening and dissipates near 25.5N-26.5W by 120 hours. Elsewhere...subtropical low pressure becomes well-defined at 33N-51W by 36 hours...dissipates near 32.5N-58.5W just after 72 hours.
0000Z ECMWF Model Run...For area of interest #1...center of surface cyclone stalls just northwest of Madeira Island from 24 to 48 hours...afterwards drifts south-southwestward while weakening and dissipates over the western Canary Islands by 120 hours. Elsewhere...subtropical low pressure becomes well-defined at 30.5N-50.5W by 48 hours...dissipates near 30N-59W just after 96 hours.
1200Z GFS Model Run...For area of interest #1...center of surface cyclone stalls just northwest of Madeira Island from 12 to 30 hours...afterwards drifts south-southwestward while weakening and dissipates at 27.5N-20W by 108 hours. Elsewhere...subtropical low pressure becomes well-defined at 31N-52.5W by 36 hours...dissipates near 30.5N-59W at 72 hours. In addition...tropical low forms in the southern Caribbean Sea near 10.2N-80.2W at 84 hours...makes landfall in southern Nicaragua at 102 hours without tropical cyclone formation.
0600Z NAVGEM Model Run...For area of interest #2...center of surface cyclone stalls just northwest of Madeira Island from 12 to 24 hours...afterwards drifts southwest while weakening and dissipates at 27.5N-22W by 114 hours. Elsewhere...subtropical low pressure becomes well-defined at 32N-52.5W by 42 hours...dissipates near 32.5N-58.5W at 84 hours.