MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #179
*******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 NOVEMBER 13 2020 3:11 PM EDT...
See remnants of Eta section below for a final statement on the frontal low pressure offshore of North Carolina that was Tropical Storm Eta. See Tropical Storm Theta and tropical depression thirty-one sections below for the two currently active tropical cyclones in the Atlantic basin.
REMNANTS OF ETA...In the early morning hours Tropical Storm Eta located offshore of the Carolinas was downgraded to a remnant non-tropical low pressure located along the cold front that has moved offshore of the eastern United States and into the northwest Atlantic. During the transition to non-tropical...the northeast half of the circulation fired a circular thunderstorm mass that has strengthened the circulation to 45 mph maximum sustained winds. This could be the combination of the warm Gulf stream waters and supporting upper divergence between the western Atlantic deep-layered ridge and fast-approaching upper trough from southern Canada. Even as we head into the afternoon...this circular thunderstorm mass has persisted. A check on the ASCAT passes however reveals an elongated wind shift offshore of the Carolinas characteristic of a cold front instead of a circular area of rotation characteristic of a tropical cyclone...which is why the National Hurricane Center considers Eta non-tropical at this point. However some strengthening of Eta's non-tropical remnant frontal low pressure is possible in the next 24 hours as it moves across the open northwestern Atlantic due to the ongoing supportive upper divergence regime ahead of the southern Canada upper trough...this is something that was hinted at in yesterday's 1200Z ECMWF and now most models agree upon. Despite this...all models also agree that at or just after 24 hours the strengthening remnant frontal low will lose its identity to a much lager frontal cyclone to form further north along the same front and in the upper divergence maximum of the upper trough. This is my final statement on Eta on this blog as it is no longer a tropical cyclone.
TROPICAL STORM THETA...As of today...Theta's surface inflow and warm core anticyclonic upper outflow remain tucked below the 200 mb layer as the upper-level winds in the above birdseye view chart...plotted all the way up at the 200 mb layer of the atmosphere...has become less anticyclonic and more linear. This could be why Theta's thunderstorms have had relative symmetry around the center despite blowing straight from the west at the 200 mb layer...as the storm's structure has not been tall enough to be sheared by the 200 mb upper winds. Instead the 200 mb upper wind field has been advanatageous to Theta by being divergent in nature on the east side of the central Atlantic upper trough...which is likely why Theta has been able to fire another round of thunderstorms and keep its tropical nature despite being over cooler 22 deg C waters and under upper-level temperatures that are not very cold (the 200 mb heights over Theta measure 1212 dekameters...would like to see 1200 or less for an indication of cold de-stabilizing upper air temps when the water temps are in the low 20s of deg C).
Updated forecast track is unchanged in the short-term as Theta has been on par with the previous forecast...and should continue eastward in tandem with its supporting central Atlantic upper trough. By 24 and 48 hours the upper trough is forecast to elongate into a strip of upper vorticity due to the strength of the deep-layered ridge to the west...and I forecast Theta to nearly stall west of the Canary Islands by that time in between conflicting steering of the deep-layered ridge and a surface ridge forecast to be over Europe to the east and supported by the western convergence zone of the pair of north and northeast Atlantic upper troughs as those troughs move into Europe. Albeit I have shifted the longer term forecast a little eastward due to the latest model consensus that brings Theta a little closer to the Canary Islands...perhaps as the deep-layered ridge is forecasted to be a little more east with the latest data input into the models. It is also during this time that I forecast Theta to weaken and gradually lose its tropcial characteristics as it will no longer have upper divergence to help it...instead it will be exposed to a lack of divergence beneath the upper vorticity strip and eastern upper convergence zone of the deep-layered ridge. With this paradigm...I am in agreement with the NHC intensity forecast. I have ended the forecast at 48 hours as this when its most likely that Theta will have lost its warm core after its thunderstorm dissipate in the upper-level convergence and unfavorable thermodynamic environment (cool waters...not so cold upper air temps). After 48 hours...whatever is left of Theta will be pulled northward into a large north Atlantic frontal cyclone to later develop with the support of the current southern Canada upper trough as that trough moves into the north Atlantic.
Theta will continue to have potential to produce coastal sea swells on the shores of the Canary Islands and Azores. After Theta loses its thunderstorms and warm core upper outflow...it will require time to weaken and therefore may still produce some gusty winds over the Canary Islands on Sunday or Monday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Nov 13)...60 mph maximum sustained wind tropical storm centered at 31.7N-23.8W
IOH 24 Hr Forecast (1200Z Nov 14)...50 mph maximum sustained wind tropical storm centered west of the Canary Islands at 31.5N-20.5W
IOH 48 Hr Forecast (1200Z Nov 15)...40 mph maximum sustained wind remnant low centered just west of the Canary Islands at 31.5N-19W
TROPICAL DEPRESSION THIRTY-ONE...Through the morning hours...the south side of the tropical wave of low pressure in the central Caribbean Sea developed increased and organized thunderstorms and has intensified into the thirty-first tropical depression of this hyperactive 2020 Atlantic Hurricane Season. The thunderstorm activity and upper outflow on the north and west sides of the circulation have been limited by a southwest-to-northeast oriented upper trough located in the region... but this upper trough is weak enough such that the depression has continued to become better organized and will likely be upgraded to a tropical storm by 4 PM EDT...and if not later this evening.
The westward track of the new tropical cyclone has been slow due to the surface ridge weakness created by the remnants of Eta. An increase in forward speed is expected by 24 hours from an eastern US surface ridge to build in the wake of Eta and southern Canada upper trough to exit the region. By 48+ hours... the current upper vorticity offshore of Alaska and western Canada is forecast to arrive into the eastern North America as a strong upper trough whose eastern divergence zone creates a strong frontal cyclone and whose western convergence zone creates a strong surface ridge over the south-central United States. The forecast position of the frontal cyclone is too far north to influence the steering...therefore it is likely in the longer term that this tropical cyclone’s westward track continues but remains slow due to the blocking effect of the forecast south-central United States surface ridge...potentially bending on a southward angle from the strength of the surface ridge as the tropical cyclone moves into Nicaragua and Honduras. My short-term forecast track is adjusted southward as the tropical depression has been consolidating toward the stronger thunderstorm activity in the southeast half of the circulation...but in the long term is kept much the same as the models this morning seemed to have adjusted the forecast track northward more toward Honduras.
The southwest-northeast weak upper trough crossing through the north half of this tropical cyclone should be gradually weakening from the latent heat release of the cyclone's thunderstorms...therefore the upper outflow of this tropical cyclone should improve with time. I forecast slower strengthening for the first 24 hours to give time for the upper trough to dissipate....followed by rapid strengthening given the favorable upper wind outlook... strong computer model support...and warm Caribbean waters. My intensity forecast has increased given that this system has already formed into a tropical depression...and now brings this system to category 4 major hurricane strength just before landfall in Nicaragua and Honduras.
Needless to say...this forecast is exceptionally terrible news as we are likely in for severe tropical cyclone impacts in Nicaragua and Honduras only recently after Hurricane Eta devastated this region with powerful winds and catastrophic rainfall flooding...and unfortunately interests here need to be aware of this tropical depression. The chances for heavy rainfall for Jamaica have reduced as the current upper trough in the region has limited the thunderstorm activity on the north side of this system's circulation.
*******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Nov 13)...35 mph maximum sustained wind tropical depression centered in the central Caribbean Sea at 14.2N-74.3W
IOH 24 Hr Forecast (1200Z Nov 14)...60 mph maximum sustained wind tropical storm centered in the central Caribbean Sea at 14.2N-78W
IOH 48 Hr Forecast (1200Z Nov 15)...100 mph maximum sustained wind hurricane centered in the central Caribbean Sea at 14.2N-80.5W
IOH 72 Hr Forecast (1200Z Nov 16)...135 mph maximum sustained wind major hurricane centered just offshore of northeastern Nicaragua at 14N-82.5W
IOH 96 Hr Forecast (1800Z Nov 17)...60 mph maximum sustained wind tropical storm centered over northern Nicaragua at 13N-85W
IOH 120 Hr Forecast (1800Z Nov 18)...Remnant low pressure centered over the south tip of Honduras and just east of El Salvador at 12.8N-87.5W
...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 Theta...stalls just west of the Canary Islands from 48 to 66 hours while weakening...circulation weakens to a remnant trough at 37.5N-18W at 102 hours. For tropical depression thirty-one...passes just offshore of eastern Honduras at 84 hours as a strong hurricane...while reaching northwest coast of Honduras weakens to a tropical storm by 108 hours...weakens to an inland remnant low centered on the northern Honduras/Guatemala border by 132 hours.
0000Z ECMWF Model Run...For Tropical Storm Theta...stalls just west of the Canary Islands from 48 to 72 hours while beginning to weaken...circulation weakens to a remnant surface trough located north of the Canary Islands at 36.5N-18W just after 96 hours. For tropical depression thirty-one...makes landfall at the Nicargua/Honduras border as a compact hurricane between 72 and 96 hours...weakens to a remnant low reaching the Pacific coast of El Salvador by 120 hours.
1200Z GFS Model Run...For Tropical Storm Theta...stalls just west of the Canary Islands from 48 to 60 hours while weakening...circulation weakens to a remnant trough just northeast of Madeira Island at 36N-15W at 90 hours. For tropical depression thirty-one...makes landfall over eastern Honduras as a strong hurricane at 96 hours...weakens to a remnant low over the northwest coast of Honduras at 126 hours. Elsewhere...tropical wave currently at 56W becomes a compact tropical low pressure in the southern Carribean Sea at 12.5N-76W at 138 hours...becomes a compact tropical cyclone in the long range.
0600Z NAVGEM Model Run...For Tropical Storm Theta...passes just northwest of Madeira Island at 60 hours while weakening...weakens to a remnant surface trough at 40N-15W at 90 hours. For tropical depression thirty-one...passes just north of the Honduras coast by 120 hours as a strong hurricane...makes landfall in Belize in the long range.