*******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 AUGUST 13 2020 4:30 PM EDT...
See Tropical Storm Josephine section below for the only active tropical cyclone in the Atlanic basin.
Elsewhere...the cold front currently over the eastern United States is approaching the western Atlantic basin...and a surface low pressure with thunderstorms just ahead of the front and over coastal North Carolina appears to be already forming with the support of outflow from a warm upper ridge also located just ahead of the front...therefore the National Hurricane Center has just introduced this feature as an area of interest for tropical cyclone development in the coming days. See area of interest section below for additional details.
TROPICAL STORM JOSEPHINE...Tropical depression eleven has recently strengthened into Tropical Storm Josephine with the support of upper outflow induced by a cell of tropical upper ridging in the region. The thunderstorm activity however remains somewhat biased northwest of the center as the cell of upper ridging also appears to be inducing some southeasterly vertical shear. With the exception of the ECMWF model which shows some strengthening in the next 24 hours...most of the models indicate that Josephine will not significantly strengthen in the short term. Thus I have only slightly raised my intensity forecast...with the assumption that the majority model consensus are picking up on continued southeasterly shear negatively affecting Josephine...perhaps with some dry saharan air to the east perhaps also getting driven toward Josephine by the shear. All models are in agreement that Josephine will weaken while passing just north of the northeastern Caribbean islands...to be caused by stronger westerly shear to be induced by the upper trough currently spanning the Gulf of Mexico and western Atlantic. Thus I forecast Josephine to weaken to a remnant low pressure by 96 hours.
Regarding the track forecast...I have nudged the track points northwestward due to the current position and heading of Josephine. A curve to the north in the track is shown by 72 to 96 hours as the current frontal zone over the eastern United States will erode the west side of the steering Atlantic surface subtropical ridge.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 13)...45 mph maximum sustained wind tropical storm centered at 13.7N-49.2W
IOH 24 Hr Forecast (1200Z Aug 14)...50 mph maximum sustained wind tropical storm centered at 15N-54.5W
IOH 48 Hr Forecast (1200Z Aug 15)...50 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 16.5N-59W
IOH 72 Hr Forecast (1200Z Aug 16)...35 mph maximum sustained wind tropical depression centered just north of the Virgin Islands at 20N-64.5W
IOH 96 Hr Forecast (1200Z Aug 17)...Remnant surface low pressure centered in the western Atlantic at 24.5N-67W
AREA OF INTEREST #1...A surface cold front over the eastern United States and its associated upper trough over eastern Canada are currently advancing into the northwestern Atlantic. Just out ahead of this front...and over coastal North Carolina...a surface low pressure spin with organizing thunderstorm bands has formed with the support of upper outflow beneath a warm upper ridge also located ahead of the front. All models agree that this system will slide east-northeastward away from North Carolina and into the open northwestern Atlantic while swept up by the front...presenting it as an elongated low pressure along the front by 72 hours. The aforementioned upper trough is expected to elongate southwest-to-northeast while stretched by a warm upper ridge to build over eastern Canada...with the elongated upper trough to increasingly shear this system by 48+ hours. The divergence zone of this elongated upper trough will also likely strengthen this system non-tropically as it moves into the open northwestern Atlantic. I give a modest 30% odds of tropical cyclone formation in the next 24 hours given the organizing nature of the thunderstorm bands...then drop the odds of development toward 0% by 72 hours as the increasing shear makes conditions hostile for tropical development...and as the frontal zone overspreads the circulation and makes this system less tropical...especially as the elongated upper trough strengthens it by non-tropical means.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 14)...30% chance of tropical cyclone formation (just east of Cape Hatteras North Carolina near 35N-75W)
IOH 48 Hr Outlook (1200Z Aug 15)...10% chance of tropical cyclone formation (northwestern Atlantic near 37.5N-71W)
IOH 72 Hr Outlook (1200Z Aug 16)...0% chance of tropical cyclone formation (northwestern Atlantic near 40N-65W)
...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 Josephine...opens into a remnant trough of low pressure just northeast of the Bahamas in 96 hours. For area of interest #1...low pressure currently over coastal North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 40N-61.5W by 72 hours (elongated nature indicates system is non-tropical and frontal in nature)
1200Z ECMWF Model Run...For Tropical Storm Josephine...strengthens as a compact tropical cyclone near 17N-54W in 24 hours...weakens while passing just northeast of the Lesser Antilles near 19.5N-60W in 48 hours...dissipates north of Puerto Rico near 21.5N-66W in 72 hours. For area of interest #1...low pressure currently over coastal North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 40N-64W by 72 hours (elongated nature indicates system is non-tropical and frontal in nature)
1200Z GFS Model Run...For Tropical Storm Josephine...opens into a remnant trough of low pressure just northeast of the Bahamas in 96 hours. For area of interest #1...low pressure currently over coastal North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 40.5N-62.5W by 72 hours (elongated nature indicates system is non-tropical and frontal in nature)
1200Z NAVGEM Model Run...For Tropical Storm Josephine...curves tropical storm west-northwest across the western Atlantic with no strengthening shown...and reaches the waters northeast of the Bahamas at 24N-69W in 120 hours. For area of interest #1...low pressure currently over coastal North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 38N-62.5W by 72 hours (elongated nature indicates system is non-tropical and frontal in nature)
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