*******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 AUGUST 4 2020 3:09 PM EDT...
See Tropical Storm Isaias section below for the only active tropical cyclone in the Atlantic basin. See area of interest section below for a surface trough of low pressure in the western Atlantic being monitored for development.
TROPICAL STORM ISAIAS...Just before landfall last night just west of the Cape Fear region of North Carolina...Isaias was able to briskly intensify into an 85 mph maximum sustained wind hurricane as the shear reduced ahead of the amplifying upper trough incoming to the west (the upper flow ahead of the trough became more southerly and aligned with the storm track...hence lowering the shear). It is also probable Isaias strengthened as cool northerly flow on its west side has amplified the cold core upper trough...with increased divergence on the east side of the upper trough in turn re-enforcing the surface low pressure center of Isaias. This same process has moreso taken hold as Isaias has been flung rapidly north-northeast across eastern North Carolina...southeast Virginia....eastern Maryland...and now into the Pennsylvania/New Jersey border with Isaias incredibly still a high-end tropical storm even with all the land interaction. This track is further west than forecast yesterday...likely as Isaias's western cool northerly flow has amplified the upper trough more than forecast...which makes the steering flow ahead of the upper trough more southerly and less westerly. My updated forecast track is thus adjusted westward with the latest model guidance...taking the circulation across eastern New York state and into Quebec. Isaias will soon be declared non-tropical as it continues to maintain strength primarily with the aid of the upper trough...and the model guidance insists that a seperate frontal low in the vicnity of the Quebec/Ontario border will quickly develop in the next 24 hours and absorb Isaias while becomign the dominant. Therefore in addition to impacts across the northeastern United States...we can now expect potential for gusty winds in eastern Ontario and southern Quebec from the remnants of Isaias and the seperate frontal low.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 4)...65 mph maximum sustained wind tropical storm centered over the Pennsylvania/New Jersey Border at 40.5N-75W
IOH 24 Hr Forecast (1200Z Aug 5)...Remnant frontal low centered over Quebec at 50N-74W
AREA OF INTEREST #1...The western Atlantic surface trough of low pressure passing through the western Atlantic between Bermuda and the Caribbean Islands has continued to see a reduced amount of thunderstorm activity...perhaps this has been from southeasterly flow from upper vorticity to the west converging with easterly flow from the western Atlantic upper ridge axis located just to the north...with this upper convergence making some dry sinking air around this disturbance. Despite this...the surface trough appears to be producing an increasingly defined spin in the vicinity of 28N-68W. However odds of development are decreasing as the upper trough steering Tropical Storm Isaias north-northeast will soon merge with the upper vorticity to the west...and will also push the vorticity toward the disturbance...which will likely begin to increase unfavorable wind shear. Forecast track is a slow west-northwest to northwest progression around the west side of the Atlantic subtropical ridge...with the track slow because the upper trough interacting with Isaias will pass to the north and its western convergence zone will produce another surface ridge over the Great Lakes region of North America blocking the disturbance's progress around the Atlantic subtropical ridge. Isaias's remnant low will leave behind a trailing cold front that will be sandwiched between the two surface ridges...and I show the disturbance drifting north toward the trailing front as it approaches in 96 hours. I drop odds of development to 0% by this timeframe as the front will have potential to absorb this disturbance...and the more north position of the disturbance will expose it to mid-latitude upper westerlies that will increase the unfavorable shear further.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 5)...35% chance of tropical cyclone formation (western Atlantic near near 31N-72W)
IOH 48 Hr Outlook (1200Z Aug 6)...20% chance of tropical cyclone formation (western Atlantic near 32N-72W)
IOH 72 Hr Outlook (1200Z Aug 7)... 20% chance of tropical cyclone formation (east of North Carolina near 33N-74W)
IOH 96 Hr Outlook (1200Z Aug 8)...0% chance of tropical cyclone formation (east of North Carolina near 36N-74W)
...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 Isaias...moves northward across souheastern Quebec while losing its identity to frontal low pressure to the west in 24 hours. For area of interest #1...no tropical cyclone formation shown. Elsewhere...tropical wave currently emerging from western Africa becomes tropical low pressure near 12.5N-38W in 126 hours...becomes tropical cyclone near 11.5N-41W by 180 hours.
0000Z ECMWF Model Run...For Tropical Storm Isaias...moves northward across eastern Quebec while losing its identity to frontal low pressure to the west in 48 hours. For area of interest #1...no tropical cyclone formation shown.
0600Z GFS Model Run...For Tropical Storm Isaias...moves northward across southeastern Quebec while losing its identity to frontal low pressure to the west in 30 hours. For area of interest #1...no tropical cyclone formation shown.
0600Z NAVGEM Model Run...For Tropical Storm Isaias...moves northward across southeastern Quebec while losing its identity to frontal low pressure to the west in 36 hours. For area of interest #1...no tropical cyclone formation shown