MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #41
*******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.**********
...TUESDAY JUNE 23 2020 5:16 PM EDT...
See Tropical Storm Dolly section below for the only active tropical cyclone in the Atlantic basin.
Elsewhere...impressive bursts of thunderstorm activity have been occuring in the northwestern Gulf of Mexico as the south part of a longwave upper trough over central North America is becoming cut-off into a small upper vortex over the northwest Gulf due to the strength of a longwave upper ridge that extends from the eastern Pacific offshore of Baja California and into the western United States. Current thunderstorm bursts south of Louisiana are being driven by the divergence on the east side of the upper vortex...and the bursts further west offshore of the Texas coast and directly below the upper vortex are due to the instability caused by warm Gulf of Mexico waters coupled with the cool temps of the upper vortex. Further inland and to the north...over eastern Oklahoma and northeastern Texas...another rotation of clouds and thunderstorms is associated with a frontal low pressure that has materialized in a zone of upper divergence between northerlies flowing into the northwestern quadrant of the upper vortex and westerlies flowing across the central North America longwave upper trough axis. ASCAT-A ascending and descendign passes suggest a surface rotation just south of Galveston Bay Texas. The ECMWF and GFS model runs in the computer model summary below suggest a surface low pressure consolidating just inland of the Texas coast over the next day or so...therefore not considering this feature as an area of interest for tropical cyclone development unless it is more clear a coastal or offshore circulation will or is maturing. Based on the ECMWF and GFS as well as current observations...it appears that the northeast Texas frontal low and possible surface rotation just offshore of Galveston Bay will merge inland...possibly producing thunderstorms with flash flooding over eastern Texas...Louisiana...and Arkansas over the next couple of days...and perhaps behave like an inland tropical system should it sustain itself with the outflow of upper ridging adjacent to the northwest Gulf upper vortex...especially if the remainder of the longwave upper trough over central North America stays far north enough to not shear this system.
TROPICAL STORM DOLLY...Subtropical depression four located in the open northwestern Atlantic and beneath a cut-off upper vortex as of this morning has developed bursts of showers and thunderstorms over its center with cirrus outflow clouds courtesy of the instability provided by the warm Gulf stream waters and cool temperatures of the upper vortex. As a result by the early afternoon...the National Hurricane Center has indicated the depression has strengthened into a fully tropical storm...with the cirrus outflow indicating the formation of warm core upper outflow generated by the latent heat release of the thunderstorms...with the outflow allowing for strengthening. It should be noted the outflow is not present at the 200 mb upper layer of the atmosphere...so this system is a shallow tropiacl cyclone with the surface circulation and upper outflow tucked beneath the upper vortex. The next name on the Atlantic list is Dolly...making it one of the earliest fourth named storms of an Atlantic hurricane season (previous record holders were Dennis in 2005 when it got named on July 5th...superseded by Tropical Storm Debby in 2012 when it got named on June 23...then superseded by Tropical Storm Danielle in 2016 when it got named on June 20). True-color visible satellite shows a banding-type eye feature in the small circulation...so it would not surprise me if Dolly is currently a bit stronger than its 1 PM EDT rating of 45 mph maximum sustained winds. Computer models are in strong agreement that by 1200Z tomorrow Dolly's surface center should be tracking northeastward near 42N-58.5W...and satellite animation is beginning to show a more northeast track beginning. This is due to the steering effects of a deep-layered ridge materializing to the east as a fragment of the upper ridge off to the west has passed over southeastern Canada and to the north of the upper vortex...and is now east of Dolly and the upper vortex while aligning with the north lobe of the Atlantic surface subtropical ridge. The deep-layered ridge should steer Dolly and the overhead upper vortex in tandem. I forecast dissipation into a remnant low by 24 hours as the forecast track will take Dolly over much cooler waters...removing the instability Dolly has thrived upon.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Jun 23)...45 mph maximum sustained wind tropical storm centered at 39.4N-61.7W
IOH 48 Hr Forecast (1800Z Jun 24)...Remnant low centered at 42.5N-58W
...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 Tropical Storm Dolly...has dissipation southeast of Nova Scotia by 24 hours
1200Z ECMWF Model Run...For Tropical Storm Dolly..located at 41.5N-58.5W by 24 hours...disspated by 48 hours. Elsewhere...develops slow-moving surface low just north of the southeast Texas coast over the next 48 hours...moves northeastward into Arkansas by 72 hours while weakening.
1200Z GFS Model Run...For Tropical Storm Dolly...located at 42N-58.5W by 24 hours...disspated south of Newfoundland by 36 hours. Elsewhere...develops surface low just north of the southeast Texas coast in 18 to 24 hours.,.loses its identity over the Texas/Louisiana border by 48 hours.
1200Z NAVGEM Model Run...For Tropical Storm Dolly...located at 42N-58.5W by 24 hours...disspated south of Newfoundland by 36 hours.