*******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 MAY 17 2020 9:36 PM EDT...
See Tropical Storm Arthur section below for details on the only active tropical cyclone in the Atlantic basin. Elsewhere...longer-range model runs continue to show the strong upper trough currently heading to the Great Lakes from the central United States settling inland over the southeastern United States rather than offshore. Therefore subtropical development in the western Atlantic in the wake of Arthur is not expected. TROPICAL STORM ARTHUR...Tropical depression one located east of Florida yesterday afternoon/evening has become Tropical Storm Arthur as expected. The tropical storm is continuing more north and less east in track as a pair of western Atlantic surface ridges blocks eastward progress out to sea. Atmospheric conditions have become more favorable for Arthur over the last day as warm upper ridging amplifies over the storm due to warm air advection out ahead of a new Great-Lakes-Bound frontal low pressure system over the central United States. The upper ridging is allowing for Artur to be in a low shear environment with supportive upper anticyclonic outflow. But Arthur is reminding us that it is still not yet hurricane season as the thunderstorm activity has actually become less intense in the circulation...because the warm Gulf stream waters which are just at the threshold to support tropical development have not been enough to allow Arthur to strengthen beyond 45 mph maximum sustained winds. Therefore my updated intensity forecast is lowered from the previous...showing no additional strengthening going forward. A tropical storm warning is in effect for the Outer Banks of North Carolina where the center of Arthur should pass very close to in the next 24 hours. Preparations here for tropical storm conditions should have been completed by now...albeit if current trends continue (where Arthur does not strenghten) the risk of wind damage will be low...however for beachgoers the risk of surf and rip currents here and along the United States east coast should be taken seriously. The early part of my forecast is adjusted slightly northeastward due to Arthur's position at 1800Z with respect to the previou forecast. By 48+ hours...the persistent upper vortex in the north Atlantic that has been south of Greenland will help swing an upper trough toward the southeastern Canadian coast. Divergence out ahead of this upper trough will create a weakness in the western Atlantic surface ridging that will likely draw Arthur eastward away from the United States east coast after it brushes the North Carolina outer banks. However convergence on the back side of the upper trough will create another surface ridge to the north...which combined with the western Atlantic surface ridging will make the weakness fairly narrow. The NAVGEM...CMC...Euro...and GFS models have come into better agreement in Arthur's long range track...with the consensus among all four suggesting Arthur will initially swing east and then perhaps loop back southwestward as the ridge weakness closes. This is similar to the track forecast I came up with yesterday...so my updated forecast track shows this solution. Upper westerly winds ahead of the upper trough expected over southeastern Canada will likely shear Arthur...so I show a slightly lower forecast intensity at 48 to 72 hours...albeit this intensity could be generous given Arthur's current satellite appaerance...in other words I would not be surprised if Arthur dissipated into a remnant low pressure during this timeframe. I show dissipation to a remnant low at 96 hours as the southwestward drift would move this system out of the Gulf stream into cooler waters. ******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast*********** 0 Hr Position (1800Z May 17)...45 mph maximum sustained wind tropical storm centered offshore of the southeastern United States at 31.5N-77.2W IOH 24 Hr Forecast (1800Z May 18)...45 mph maximum sustained wind tropical storm centered just northeast of Cape Hatteras North Carolina at 35.5N-74.5W IOH 48 Hr Forecast (1800Z May 19)...35 mph maximum sustained wind sheared tropical depression centered at 37N-70W IOH 72 Hr Forecast (1800Z May 20)...35 mph maximum sustained wind sheared tropical depression centered at 36N-65W IOH 96 Hr Forecast (1800Z May 21)...Remnant low pressure centered at 34N-68W