MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #164
*******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.**********
...THURSDAY OCTOBER 29 2020 12:40 PM EDT...
See Tropical Storm Zeta section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest section below for the tropical wave of low pressure approaching the Caribbean Sea being monitored for development.
TROPICAL STORM ZETA...Zeta continues racing northeastward in a strong jet of upper southwesterly winds ahead of a southern United States surface frontal low and its supporting upper trough. It is surprising that Zeta is still considered a tropical storm with 50 mph maximum sustained winds this far inland...as it has moved far from southeast Louisiana and into the Applachian Mountain region of North Carolina and Virginia in the last 24 hours. The tropical aspect of Zeta is due to its central shower and thunderstorm activity (which at this point is supported by the eastern divergence zone of the upper trough) whose latent heat release is still producing a warm core...but this warm core will be wiped out once Zeta officially merges with the front tied to the east side of the southern US frontal low due to the cold air north of the front. There are mutliple reasons Zeta is and will continue to produce high winds even as it loses tropical characteristics...(1) Zeta's surface low pressure will remain supported by the eastern divergence zone of the upper trough ...(2) the unexpected strengthening of Zeta before its landfall yesterday afternoon and fast northeast track has not given the storm enough time to weaken before moving well inland...(3) the fast northeast track has accelerated the wind speed on the southeast half of the circulation while reducing the wind in the northwest side...as such the southeast side of Zeta will spread gusty tropical storm force winds across the Carolinas...southern Virginia...and southeastern Maryland. Heavy rainfall with some flash flooding potential is also possible across all aforementioned land areas...as well as northern Virginia...the rest of Maryland...and Delaware.
Forecast track below is in agreement with many of the model runs that take Zeta rapidly into the open northwest Atlantic as a remnant frontal low over the next 24 hours. There is disagreement on exactly when Zeta will lose its identity along this front...or another front (currently over eastern Canada) to overrun Zeta in about a couple of days.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Oct 29)...50 mph maximum sustained wind tropical storm centered over the western North Carolina/Virginia border at 36.5N-81.5W
IOH 24 Hr Forecast (1200Z Oct 30)...Remnant frontal low centered over the open northwestern Atlantic at 40N-60W
AREA OF INTEREST #1...The tropical wave of low pressure that was previously approaching the Lesser Antilles has crossed the island chain and entered the eastern Caribbean Sea. However the heaviest and widespread squalls of showers and thunderstorms are sheared off to the east of the islands by the current western Atlantic upper vorticity...and this is also where the upper divergence on the east side of the upper vorticity string is also higher. This activity has also become more widespread towards the east as surface convergence provided by another tropical wave near 52.5W has also helped to boost activity. Therefore I have nudged my updated forecast points eastward while assuming the area of lowest surface pressure will form toward the thunderstorm squalls and east of the tropical wave currently near the Lesser Antilles. While remaining cut-off from high-latitude cold air while squashed on the south side of the warm upper ridge entering the western Atlantic...the cold core upper vorticity string is forecast to weaken and break up...with this disturbance finding more favorable upper winds (low shear and upper outflow) beneath an anticyclone to expand in between the fracturing vorticity. My odds of tropical cyclone formation are increased to a high 70% and towards day 5 as this is when the GFS...CMC...NAVGEM...and ECMWF models all currently agree that a tropical cyclone will have formed. However I also begin to lift odds above 0% as soon as 48 hours when the expanding upper anticyclone will already be materializing and dropping shear levels. The models are in disagreement on the formation point and eventual track...with the CMC and NAVGEM showing a more northern track...and the GFS and ECMWF showing a more southern track. My forecast leans toward the GFS and ECMWF which are historically better models for tropical cyclones. Regardless of which model is selected...all are in agreement that the current upper trough south of Alaska will pivot across North America by the end of the 5-day forecast period ...and the western convergence zone of this strong upper trough is forecast to build a strong surface ridge to the northwest of this disturbance that will slow its westward track and add a southward component to the track angle. Because of the more reliable GFS and ECMWF models showing a more southward formation point and because of the forecast surface ridge by day 5...it is most probable that tropical cyclone impacts will occur for Central America (particularly Nicaragua and Honduras) instead of the northern Caribbean Islands...and interests here should be paying close attention to this disturbance.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 30)...0% chance of tropical cyclone formation (southeastern Caribbean Sea near 12N-65W)
IOH 48 Hr Outlook (1200Z Oct 31)...10% chance of tropical cyclone formation (south-central Caribbean Sea near 12.5N-70W)
IOH 72 Hr Outlook (1200Z Nov 1)...30% chance of tropical cyclone formation (south-central Caribbean Sea 13N-75W)
IOH 96 Hr Outlook (1200Z Nov 2)...50% chance of tropical cyclone formation (east of Nicaragua and Honduras near 13.5N-80W)
IOH 120 Hr Outlook (1200Z Nov 3)...70% chance of tropical cyclone formation (just east of Nicaragua near 13N-82.5W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...For Tropical Storm Zeta...transitions to remnant frontal low that loses its identity along the front while over the open northwestern Atlantic in 42 hours. For area of interest #1...tropical wave strengthens to a surface low in the central Caribbean Sea near 16N-72.5W by 60 hours...tropical cyclone formation suggested shortly thereafter...tropical cyclone makes landfall in Jamaica at 90 hours...makes landfall in the Cayman Islands at 108 hours...strong surface ridge to the northwest pushes tropical cyclone southwestward away from the Cayman Islands in long range while tropical cyclone intensifies.
0000Z ECMWF Model Run...For Tropical Storm Zeta...transitions to remnant frontal low that loses its identity along the front while over the open northwestern Atlantic in between 24 and 48 hours. For area of interest #1...tropical wave organizes into a tropical low pressure in the central Caribbean Sea near 14N-74W at 72 hours...tropical cyclone formation suggested between 96 and 120 hours...tropical cyclone makes landfall on Nicaragua/Honduras border at 120 hours.
0600Z GFS Model Run...For Tropical Storm Zeta...transitions to remnant frontal low while moving into the open northwestern Atlantic in the next 24 hours...current front to the northwest over eastern Canada develops a frontal cyclone whose cold front absorbs the remnants of Zeta in the open north Atlantic by 60 hours as Zeta loses its identity. For area of interest #1...tropical wave strengthens to a surface low in the central Caribbean Sea near 14N-77.5W by 78 hours...tropical cyclone formation suggested near 13.5N-79.5W by 114 hours...tropical cyclone reaches intense strength in long range while drifting west-southwest into the east coast of Nicaragua.
0600Z NAVGEM Model Run...For Tropical Storm Zeta...transitions to remnant frontal low while moving into the open northwestern Atlantic in the next 24 hours...current front to the northwest over eastern Canada develops a frontal cyclone whose cold front absorbs the remnants of Zeta in the open north Atlantic by 54 hours...Zeta retains its identity along this cold front while moving over the northern British Isles by 78 hours. For area of interest #1...tropical wave strengthens to a surface low in the central Caribbean Sea near 16N-69W by 48 hours...surface low moves over Jamaica by 84 hours...tropical cyclone formation suggested just south of the Cayman Islands by 102 hours...strong surface ridge to the northwest pushes tropical cyclone southwestward into north coast of Honduras in long range while tropical cyclone intensifies.