*******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.**********
...MONDAY JUNE 29 2020 4:59 PM EDT...
See area of interest sections below for areas in the tropical Atlantic being monitored for tropical cyclone development by the National Hurricane Center. Elsewhere...the models have recently trended in showing a surface low pressure forming offshore of the southeastern United States in 3 to 4 days in response to a stronger than previously thought central North America upper ridge that pushes the upper vortex currently over southeastern Canada to a further south position toward the southeastern United States..with the offshore surface low forming in the supportive eastern divergence zone of the upper vortex. If such a disturbance forms...it is likely to shift east-northeastward into the open western Atlantic as the upper vortex itself shifts offshore...possibly evolving into a tropical or subtropical system. If these model trends continue into tomorrow...will mark the upper vortex as another area of interest for potential tropical or subtropical development.
Computer models also suggest by next week...another subtropical or tropical disturbance could emerge over the northeastern Gulf of Mexico or western Atlantic waters offshore of the southeastern United States in response to the current shortwave upper trough over the southwestern United States that has potential to become another upper vortex over the southeastern United States cut-off from the mid-latitude westerlies by the central North America upper ridge. Will wait to see if this model trend persists in the coming days before declaring yet another area of interest.
AREA OF INTEREST #1...A vigorous tropical wave of low pressure in the central tropical Atlantic has curiously taken on a southwest-to-northeast tilt on satellite imagery in the last 24 hours...with a persistent area of loosely packed showers and thunderstorms to the southwest that shows some signs of rotation...and another area of rotation to the northeast at the apex of the wave that has seen an increase in concentrated thunderstorms this afternoon. In addition southeasterly flow on east side of the wave axis appears to have kinked the dry saharan air locally northward and away. Although these observations might seem positive for tropical development...ASCAT passes have not shown a closed ciruclation developing in either the southwestern and northeastern regions of the broad wave...and the northeastern apex feature which has the most concentrated thunderstorms at the moment does not seem to be developing a closed spin including in long-term visible satellite loops. Therefore at this time I am maintaining 0% odds of tropical cyclone formation given that the tropical wave is heading toward dry saharan air off to the northwest...and that just after 48 hours will move into unfavorable westerly shearing upper winds being generated by central Atlantic upper vorticity. For the northeastern apex feature closer to the upper vorticity...shear may increase sooner than 48 hours...albeit the GFS model run suggested the upper vorticity will gradually shrink as it remains cut-off from high-latitude upper troughs that would otherwise help re-enforce it...which may keep shear levels lower for the northeastern apex feature. Will continue to watch for signs of a closed circulation in the northeastern or southwestern regions of the tropical wave...if this were to occurr I would increase short-term odds of tropical cyclone development before the tropical wave hits higher wind shear after 48 hours.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 30)...0% chance of tropical cyclone formation (tropical Atlantic near 15N-52W)
IOH 48 Hr Outlook (1800Z Jul 1)...0% chance of tropical cyclone formation (east of the Lesser Antilles near 16N-57.5W)
AREA OF INTEREST #2...The Ohio Valley thunderstorm complex that was out ahead of the northeastern United States cold front yesterday has shifted southeastward across Tennessee and North Carolina and into the waters offshore of the Carolinas. This feature seems to be joining another mass of shower and thunderstorm activity west of Bermuda being supported by the outflow of the western Atlantic upper ridge out ahead of the front...and these developments appear to be keeping surface pressures low in a broad area out ahead of the front. Even though the CMC model continues to be the only model that suggests tropical development from this disturbance while the other models do not show development...due to these observations and increasing organization of the activity west of Bermuda I have increased odds of tropical cyclone formation out ahead of the front. Any feature that develops will shift northeastawrd in the southwesterly flow ahead of the front and on the northwestern quadrant of the Atlantic surface subtropical ridge. I have shifted my forecast points in the outlook below further south closer to the activity west of Bermuda and toward the further south positions that the CMC and ECMWF suggest a surface low pressure might form in the short-term. I wait till 48 hours to show non-zero odds of development to give time for a surface low pressure spin to form since we do not have one at the moment...and this is also the timeframe this disturbance will move northeastward across the maximum temps of the warm Gulf stream waters in the region. However I have only raised odds to 15% at this time due to possible southwesterly wind shear from the front's supporting upper vortex...especially if the western Atlantic upper ridge fail to sufficiently cover the disturbance as it moves northeastward. Odds of development are dropped back to 0% by 72 hours due to arrival to cooler waters and possible hostile westerly wind shear from a jet of upper winds out ahead of the front...albeit it is also possible that this disturbance begins accelerating rapidly east-northeast during this time while entering a tight pressure gradient and strong surface steering winds between the front and Atlatnic subtropical ridge which would help reduce such shear.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 30)...0% chance of tropical cyclone formation (west of Bermuda near 32N-69W)
IOH 48 Hr Outlook (1800Z Jul 1)...15% chance of tropical cyclone formation (northwest of Bermuda near 36N-67.5W)
IOH 72 Hr Outlook (1800Z Jul 2)...0% chance of tropical cyclone formation (northwestern Atlantic near 41N-60W)
...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 area of interest #1...short-lived low pressure center shown near 12.5N-50W in 12 hours. For area of interest #2...low pressure forms near 32N-73.5W in 24 hours...opens into a surface trough located west-northwest of Bermuda by 48 hours...then redevelops a closed circulation while accelerating northeastward and reaches peak strength possibly as a tropical cyclone near 41N-62.5W in 72 hours...loses its identity along front currently over the northeastern US (later to be over southeastern Canada) while reaching the waters east-southeast of Newfoundland in 96 hours. Elsewhere...yet another surface low pressure center shown forming offshore of the Carolinas by 84 hours that gradually strengthens while shifting east-northeastward to 40N-60.5W by 144 hours.
0000Z ECMWF Model Run...For area of interest #1...short-lived low pressure center shown near 12.5N-50W in 24 hours. For area of interest #2...short-lived low pressure center shown to form near 32N-70W in 48 hours. Elsewhere...yet another surface low pressure center shown forming near 36N-70.5W in 96 hours that gradually strengthens while shifting east-northeastward to 40N-60W by 144 hours.
1200Z GFS Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no low pressure center shown to form. Elsewhere...a low pressure center shown to rapidly consolidate near 40N-60W by 114 to 120 hours.