*******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.**********
...WEDNESDAY OCTOBER 9 2019 3:51 PM EDT...
See area of interest sections below for areas being monitored for tropical and subtropical cyclone formation. Elsewhere...showers and thunderstorms have decreased in the vicnity of the southern Lesser Antilles and coastal Venezuela...but have notably flared up in the southern Caribbean Sea due to a surface tropical wave interacting with split flow upper divergence between an upper trough extending southwest from a large central Atlantic upper vortex and south side of the upper ridge axis currently extending from the northwestern Caribbean to western Atlantic. This upper trough is expected to become a cut-off small upper vortex off to the east...and the southern part of the upper trough currently over the eastern US is forecast to cut-off into another cut-off upper vortex to the west...with the latent heat release of the southern Caribbean thunderstorms potentially bolstering an upper ridge cell whose outflow is further enhanced by the two upper vortices. The GFS and CMC models have been suggesting that tropical cyclone development could occur from this pattern in the southern Caribbean...and recently the NAVGEM has joined in. If the Euro (ECMWF) model joins in showing such a solution...or if these thunderstorms persist tomorrow...then I will be introuducing this activity as yet another area of interest for tropical development in my next update. And finally...computer models have been enthusiastic about eastern Atlantic tropical development from a tropiacl wave to emerge from Africa behind area of interest #4 in the coming days...if indeed satellite imagery shows this wave having organized thunderstorms then I will also add it as an area of interest.
AREA OF INTEREST #1...The cut-off frontal deep-layered low pressure in the open central Atalntic is continuing west-southwestward under the influence of the surface and upper-level ridging to the north and west. I have nudged my forecast track eastward based on the current position of the surface circulation. Although the surface circulation of the deep-layered low will reach the surface ridge weakness of the system in area of interest #2 in the next 24 hours...I hang on to a southward angle in the forecast track as the surface circulation reaches the west side of the upper part of the circulation where some northerly upper winds could affect the steering. I then turn this system northwest by 48 hours into the ridge weakness after the surface circulation completely decouples and escapes the upper-level circulation. The surface circulation continues lacking strong thunderstorm activity...perhaps as the cold temperatures of the upper circulation (upper vortex) are not quiet cold enough for stronger thunderstorms. However in the next 24 hours this system will be tracking into warmer 26 deg C water...so I still forecast the formation of a weak subtropical cyclone but it is also possible at this point that this system never develops thunderstorms and makes the transition to subtropical. Weakening of the surface circulation is expeced in the next 24 hours as it moves into the less favorable convergent west side of the upper circulation. At 48+ hours the surface circulation is likely to lose its identity to the low pressure field of area of interest #2. So even though the circulation will move into favorable upper winds directly below an upper ridge cell induced by warm air advection ahead of area of interest #2...the massive low pressure field of area of interest #2 will likely prevent the surface circulation from staying fully closed and developing tropically by that timeframe.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
0 Hr Position (1800Z Oct 9)...Frontal low centered at 31N-50.5W
IOH 24 Hr Forecast (1800Z Oct 10)...35 mph maximum sustained wind subtropical depression centered at 30N-55W
IOH 48 Hr Forecast (1800Z Oct 11)...Remnant low centered at 31.5N-58W
AREA OF INTEREST #2...The non-tropical frontal low that was east of Cape Hatteras North Carolina yesterday has moved northeastward and intensified into a well-defined cyclone southeast of Massachusetts under the influence of increasing divergence on the east side of a sharpening upper trough approaching from the eastern US. Coastal interests in Bermuda and eastern US shore should be aware of surf and rip current potential from this system over the next few days...with preparations for isolated power outages from damaging wind...as well as ocean storm surge...being rushed to completion from coastal Massachusetts to coastal Delaware as weather and oceanic conditions here are likely to notably detereorate in the next couple of days as the frontal cyclone intensifies further. I am continuing a subtropical cyclone formation forecast as I believe conditions are going to be favorable for this frontal cyclone to acquire some tropical characteristics in the coming days. A round of amplifying warm deep-layered ridging to the west and north will be repsonsible for the amplification of the incoming upper trough...with increasing divergence on the east side of the amplifying upper trough expected to intensify the frontal cyclone further in the next 24 hours. This warm deep-layered ridging is already in its early stages as a strong surface ridge over the eastern North America is supported by convergence on the east side of the eastern Canada upper ridge...and the eastern Canada upper ridge will be amplifying in plenty of warm air advection ahead of a strong forecast frontal cyclone to form over central Canada (currently the energy for this forecast frontal cyclone lies with an amplified upper trough over central Canada). It appears the frontal cyclone has formed northeast of where I previously predicted. Basically instead of the developing frontal cyclone absorbing the tropical low (area of interest #3) approaching from the southwest and consolidating at a further southwest location...the tropical low and frontal cyclone remain two distinct entities. Thus my short-term forecast points are adjusted northward...but not eastward as I expect the deep-layered ridging to the north and tropical low to the south to cause the frontal cyclone to swing quickly westward...with the frontal cyclone absorbing the tropical low in the process. The more north position of the frontal cyclone means that it will be able to pull more cold air southward with its west side...thus allowing the incoming upper trough to amplify into a cut-off upper vortex. I believe the southwest side of the frontal cyclone will send enough cold air to the south and east such that the upper vortex will initially form just south of the frontal cyclone center...so the absoprtion of the tropcial low to the south...blocking effect of the deep-layered ridging to the west...and whirling in of the upper vortex to the south all causing the frontal cyclone to move southeast into warmer Gulf stream waters between 24 and 48 hours...so I forecast thunderstorm development and subtropical cyclone formation in 48 hours. My forecast points in the long range (48+ hours) are nudged north and west because of the current more north position of the frontal cyclone...and because the upper trough is now more likely to amplify into a vortex (and usually upper vortices move slower to the east than upper troughs). I show weakening beginning a bit earlier than before as the formation of an upper vortex in 48 hours near the surface cyclone will produce an area of unfavorable upper convergence in the vicnity of the surface cyclone...with additional weakening by 72+ hours as the vortex opens into a fast-moving upper trough such that the cyclone is likely to be trapped in the western convergence zone of the upper trough while trying to keep up with it. Cooler water temperatures at the 96 hour forecast position makes it likely that this system will have lost any subtropical characteristics by that timeframe.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
0 Hr Position (1800Z Oct 9)...Frontal cyclone centered southeast of Cape Cod Massachusetts at 38N-67.5W)
IOH 24 Hr Forecast (1800Z Oct 10)...Frontal cyclone centered just southwest of Cape Cod Massachusetts at 38N-71W)
IOH 48 Hr Forecast (1800Z Oct 11)...60 mph maximum sustained wind subtropical storm centered south of Cape Cod Massachusetts near 36.5N-70W)
IOH 72 Hr Forecast (1800Z Oct 12)...50 mph maximum sustained wind subtropical storm centered at 38N-67W
IOH 96 Hr Forecast (1800Z Oct 13)...40 mph maximum sustained wind non-tropical remnant gale centered south of Newfoundland at 43N-56W
AREA OF INTEREST #3...The surface tropical low offshore of the southeastern US continues moving northeastward toward the frontal cyclone in area of interest #2. This feature was just on the cusp of being upgraded to a weak tropical storm yesterday afternoon...and then the thunderstorm activity became less concentrated and poorly organized due to the southwesterly shear out ahead of an upper trough approaching from the eastern US. Although some small thunderstorm bursts are currently occuring near the low pressure center...the National Hurricane Center has lowered the odds of tropical cyclone formation in their latest outlook as of 2 PM EDT...as the tropical low will be heading into cooler waters and will lose its identity to the much larger and stronger frontal cyclone developing in area of interest #2. Therefore assuming the National Hurricane Center has this feature removed from its outlook by my next update tomorrow...this will be my final statement on this feature on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 9)...0% chance of tropical cyclone formation (absorbed by frontal cyclone while located near 37.5N-65W)
AREA OF INTEREST #4...The eatern Atlantic tropical wave that just emerged from the west coast of Africa is seeing a reduction in rotating thunderstorm activity due to ingestion of dry saharan air to the northwest. Therefore I have dropped my odds of tropical cyclone formation...but have not yet made them zero...as the eastern Atlantic upper ridge cell with low shear and upper outflow will remain in place while the tropical wave moves west under the influence of strong surface subtropical ridging during the 120-hour forecast period. The models have been more enthusiastic about the next tropical wave to emerge from Africa behind this one...perhaps while this tropical wave acts as a moisture buffer against the dry saharan air for the next wave.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 10)...0% chance of tropical cyclone formation (tropical Atlantic south of the Republic of Cabo Verde near 23W)
IOH 48 Hr Outlook (1800Z Oct 11)...5% chance of tropical cyclone formation (tropical Atlantic near 28W)
IOH 72 Hr Outlook (1800Z Oct 12)...10% chance of tropical cyclone formation (tropical Atlantic near 33W)
IOH 96 Hr Outlook (1800Z Oct 13)...10% chance of tropical cyclone formation (tropical Atlantic near 38W)
IOH 120 Hr Outlook (1800Z Oct 14)...15% chance of tropical cyclone formation (tropical Atlantic near 42W)