*******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 MAY 26 2020 4:20 PM EDT...
Even though the Atlantic hurricane season does not start until June 1...continuing daily birdseye view posts on the Atlantic tropics as I am monitoring two areas for potential tropical development (the National Hurricane Center is also monitoring the area of interest just east of Florida...scheduled to reach the South Carolina coast by late tomorrow...in their tropical weather outlook)...see pair of area of interest sections below for additional details.
AREA OF INTEREST #1...The surface trough of low pressure that spans the eastern Gulf of Mexico to the Atlantic waters offshore of Florida appears to be becoming better organized and quickly while developing a spin near 29N-79W...with showers and thunderstorms already beginning to form banding features around this spin. As of 8 AM EDT the National Hurricane Center had a surface spin located notably further west over Orlando Florida as stated in their tropical weather outlook...and ASCAT-B passes as well as radar earlier this morning suggested a spin trying to develop just offshore of Cape Canaveral Florida...which is still west of the rotation at 29N-79W. Thus we can assume the rotation at 29N-79W is a mid-level spin rather than a surface one at this time. This morning water vapor imagery suggested the upper trough in the Gulf of Mexico...which gave birth to this surface trough disturbance...had two vortices...one in the northeast Gulf just south of panhandle of Florida and another one over southeastern Georgia. The one over southeastern Georgia appeared to be shearing thunderstorms east of the surface trough disturbance which made conditions less favorable for tropical cyclone development. But very recently it appears the southerly flow between the western North America longwave upper trough and eastern North America upper ridge has sent this upper vortex northward and away into the western Carolinas...which has reduced shear...and this vortex apperas to be quickly boosting outflow in the northwestern quadrant of the new mid-level low pressure at 29N-79W. Combined with the outflow and low shear of the overhead eastern North America upper ridge axis and warm Gulf stream waters...conditions appear much more ripe for tropical cyclone development...thus I have sharply raised my odds of tropical cyclone formation in the next 24 hours to 50%. If the mid-level low pressure intensifies further and reaches the surface...I will do a special update with a tropical cyclone formation forecast before my next full blog update tomorrow. This disturbance will track northward from the surface flow between western Atlantic surface ridging expected to persist beneath the convergence on the east side of the upper ridge axis and a broad area of frontal low pressure over the central United States to be supported by divergence on the east side of of the western North America upper trough. This means that in 24 hours the center of the disturbance will already be approaching the South Carolina coast...and interests here and southeastern coastal North Carolina should carefully monitor the progress of this disturbance throughout the rest of today and tomorrow in case it quickly organizes further into a tropical storm capable of brining sea swells...rip currents...and gusty winds shortly after 24 hours. Heavy rain with flash flooding potential is also another hazard possible across the Carolinas and Virginia Wednesday and into Thursday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z May 27)...50% chance of tropical cyclone formation (just offshore of South Carolina near 32.5N-79W)
IOH 48 Hr Outlook (1800Z May 28)...0% chance of tropical cyclone formation (inland over the North Carolina/Virginia border near 36.5N-77.5W)
AREA OF INTEREST #2...A shortwave upper trough continues diving southeastward across the northwestern Atlantic while influenced by a longwave upper ridge located to the west over eastern North America. The eastern divergence zone of this upper trough is producing showers and thunderstorms in the open western Atlantic to the east-southeast of Bermuda. Over the next 48 hours computer models still insist that this shortwave upper trough will amplify into a cut-off upper vortex while continuing its southeastward dive...which will result in a surface low pressure forming below the increased eastern divergence zone of the upper vortex. The surface low pressure will form where water temperatures are currently running at 24 to 26 deg C...at or just below the threshold for tropical development. However the forecast cut-off upper vortex is expected to be cold enough where it can help boost thunderstorm activity...therefore the forecast surface low pressure could acquire tropical characteristics and become a subtropical cyclone. I have kept odds of subtropical development at 0% through 48 hours and begin rising odds above 0% at 72+ hours as this is when models generally agree that the surface low pressure will develop. This is also the timeframe models show the longwave upper ridge over eastern North America finally shifting eastward into the northwestern Atlantic...which should cause the cut-off upper vortex and surface low pressure to drift northwestward and then northward around the southwest side of the upper ridge. I continue to keep odds of subtropical development on the low side as models have trended weaker with the surface low pressure...perhaps because the robust longwave upper ridge with its east convergence will maintain a strong surface ridge in the western Atlantic...perhaps strong enough to make it more difficult for a surface low pressure to take hold. I start dropping odds of development back downward by 120 hours as the northward track of this system will bring it over cooler waters...and as the cut-off upper vortex opens into a trough as it begins merging with a large upper trough approaching from the northwest...which will increase wind shear unfavorable for tropical development (this upper trough is currently parked over western Canada but is expected to reach the northwest Atlantic by the end of the forecast period). Other adjustments in this outlook include an eastward shift in the forecast points both yesterday and today as the cut-off upper vortex is forecast to consolidate further east in the latest model consensus.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z May 27)...0% chance of subtropical cyclone formation (western Atlantic near 28N-55W)
IOH 48 Hr Outlook (1800Z May 28)...0% chance of subtropical cyclone formation (western Atlantic near 28N-57W)
IOH 72 Hr Outlook (1800Z May 29)...10% chance of subtropical cyclone formation (western Atlantic near 28N-59W)
IOH 96 Hr Outlook (1800Z May 30)...15% chance of subtropical cyclone formation (east-souhtheast of Bermuda near 31N-60W)
IOH 120 Hr Outlook (1800Z May 31)...5% chance of subtropical cyclone formation (northeast of Bermuda near 35N-60W)