*******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.**********
...SATURDAY OCTOBER 12 2019 4:52 PM EDT...
See Subtropical Storm Melissa section below for more information on the cyclone offshore of the northeastern United States. See area of interest sections below for all areas being monitored for tropical cyclone formation.
Elsewhere...the eastern Atlantic tropical wave previously removed as an area of interest on this blog due to ingestion of dry saharan air has made a comeback on the south edge of the dry air mass by developing a low pressure spin at 11N-37.5W with thunderstorms further south. Only the CMC model currently shows this wave developing..and barring dry air issues the upper winds could remain favorable for development as the GFS model upper wind forecast shows the unfavorable shearing central Atlantic upper vortex diminishing while staying isolated from mid-latitude upper troughs. Therefore if the tropical wave continues to organize...I will re-add it as an area of interest in my next update tomorrow...especially because it could become quiet active in the vicinity of or just east of the Lesser Antilles as it interacts with the eastern divergence zone of a forecast sharp upper trough (this trough would come together from upper vorticity from the upper trough over Melissa and current central North America upper votex getting cut off by amplifying Gulf of Mexico upper ridging).
In addition...a broad western Atlantic surface low pressure northeast of Puerto Rico with some organized thunderstorms has come together due to supportive split flow upper divergence between the western Atlantic upper ridge and west side of the central Atlantic cut-off upper vortex. However before considering this an area of interest...will have to see how this disturbace evolves over the next 72 hours while it gets disrupted by upper vorticity from the upper trough over Melissa and current central North America upper votex to get cut off by amplifying Gulf of Mexico upper ridging.
And finally...cloudiness with pockets of thunderstorms in the western Gulf of Mexico just offshore of south Texas and east-central Mexico are somewhat organized...and are triggered by a surface frontal zone extending from the current central North America deep-layered frontal cyclone. None of the computer models forecast this feature to develop into a tropical cyclone. But while underneath the outflow of an amplifying Gulf of Mexico upper ridge this disturbance could produce thunderstorm activity in the next day or so while moving westward into far south Texas and east-central Mexico under the steering influence of the southern US surface ridge
SUBTROPICAL STORM MELISSA...Melissa offshore of the northeastern US coast remains a subtropical storm while its core thunderstorm bands have re-consolidated into a small circular thunderstorm mass covering the center. The instability to produce these thunderstorms is driven by the cold upper air temperatures of the upper trough that has moved into the northwestern Atlantic from the eastern US...to a position now directly over Melissa. The deep-layered frontal cyclone over central North America has penetrated through the deep-layered ridging that has been north and west of Melissa...resulting in the upper trough over Melissa accelerating eastward...with Melissa also accelerating eastward with the upper trough. Melissa has begun weakening while losing touch with the divergence zone on the east side of the upper trough...with this zone forecast to produce another frontal low just northeast of Melissa while Melissa itself continues weakening. By 48 hours upper vorticity currently over northeast Canada will produce a much stronger frontal cyclone southeast of Greenland...therefore in the next 48 hours Melissa will continue to be dragged eastward-northeastward out to sea while channeled on the north side of the current northwest Atlantic surface ridge...and toward the aforementioned frontal low and frontal cyclone to form to the northeast. I have adjusted the forecast track south and west due to the latest GFS model run trends in the last couple of days...which shows Melissa's east-northeast acceleration being dragged down by southern US surface ridging to extend northeastward into the western Atlantic. This will keep Melissa now over the same water temperatures it is currently over...so I maintain Melissa as a subtropical storm for 24 more hours...but at 48 hours dissipate Melissa into a remnant low as the overhead upper trough loses its definition to the much colder upper vortex over central North America and upper vorticity diving from northeastern Canada...which will place Melissa in a more hostile upper westerly shear environment. Sea swells along the northeastern US coast will continue to subside as Melissa weakens and moves away...and precautions should continue unitl the swells finish subsiding.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 12)...50 mph maximum sustained wind subtropical storm centered at 38.1N-66.5W
IOH 24 Hr Forecast (1800Z Oct 13)...40 mph maximum sustained wind subtropical storm centered at 40N-60W
IOH 48 Hr Forecast (1800Z Oct 14)...Remnant low south of Newfoundland at 41N-54W
AREA OF INTEREST #1...A broad tropical low pressure with showers and thunderstorms in the southern Caribbean region is now persisting under upper outflow heading into a small upper vortex forming to the east and another small upper vortex to the northwest being left behind by the upper trough currently over Melissa. The latent heat release of these thunderstorms is also locally bolstering warm core upper ridging between the vortices...which is also helping the upper outflow. After 24 hours...the western upper vortex is expected to dissipate in the midst of warm Gulf of Mexico upper ridging that will keep upper winds favorable for tropical development...and surface ridging is expected to persist over the southern US during the forecast period to steer this disturbance west across Central America and southeastern Mexico (the surface ridging will be bolstered by upper convergence in the wake of the upper vortex supporting the current central Canada frontal cyclone...and another upper trough and surface front at 72 to 96 hours to merge with the frontal cyclonic system from the west will pass too far north with yet another surface ridge to quickly build in its wake such that a major northward turn of this disturbance is unlikely during the forecast period). I have kept my odds of tropical cyclone formation low due to a high chance of land interaction...with tropical cyclone formation possible only if a surface circulation can consolidate offshore in the northwestern Caribbean or later on the Bay of Campeche during the next 5 days. The odds are briefly dipped to a minimum of 0% at 96 hours due to land interaction with the Yucatan peninsula that will keep the entire disturbance over land.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 13)...0% chance of tropical cyclone formation (east coast of Nicaragua)
IOH 48 Hr Outlook (1800Z Oct 14)...5% chance of tropical cyclone formation (Nicaragua...Honduras...northwestern Caribbean Sea)
IOH 72 Hr Outlook (1800Z Oct 15)...10% chance of tropical cyclone formation (northwestern Caribbean...western Honduras...and just east of Belize)
IOH 96 Hr Outlook (1800Z Oct 16)...0% chance of tropical cyclone formation (western Yucatan peninsula of southeastern Mexico...northern Guatemala...and eastern Bay of Campeche)
IOH 120 Hr Outlook (1800Z Oct 17)...5% chance of tropical cyclone formation (southeastern Mexico...Bay of Campeche)
AREA OF INTEREST #2...The National Hurricane Center in its 5-day tropical weather outlook continues mentioning the active tropical wave currently over western Africa due to various models suggesting tropical cyclone formation from this feature as it later moves offshore and toward the Republic of Cabo Verde Islands. Upper winds initially will be favorable for tropical development due to persistent eastern tropical Atlantic upper ridging with low shear and upper outflow. In the short-term it appears the eastern divergence zone of the large north Atlantic upper trough will produce enough of a surface ridge weakness such that any surface low pressure spin from this tropical wave is shown in the modeling to arrive at a further north location...toward 15N latitude. Given the recent surges of dry saharan air at that north of a location that have suppressed recent African tropical waves...I have kept my odds of tropical cyclone formation low...and my forecast positions below have a westward bias relative to the models with the current assumption that a tropical cyclone will most likely not form. However still plenty of today's model runs are gung-ho about showing quick tropical cyclone formation such that a sharp northward turn over or even east of the Republic of Cabo Verde Islands occurs...with those runs suggesting the forecast tropical cyclone is strong/tall enough to be steered by a cut-off upper trough to be left behind by the large north Atlantic upper trough. I view this cut-off upper trough as another negative against development due to southwesterly shear it would provide...especially by 96 hours when I currently end my outlook...but it is worth noting that indeed if a strong/tall enough tropical cyclone gets going and quickly turns north...the direction of travel would also keep the southwesterly shear lower.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 13)...0% chance of tropical cyclone formation (west coast of Africa and east of the Republic of Cabo Verde near 15N-18W)
IOH 48 Hr Outlook (1800Z Oct 14)...5% chance of tropical cyclone formation (just east of the Republic of Cabo Verde Islands near 15N-21W)
IOH 72 Hr Outlook (1800Z Oct 15)...5% chance of tropical cyclone formation (over the Republic of Cabo Verde Islands near 16N-24W)
IOH 96 Hr Outlook (1800Z Oct 16)...0% chance of tropical cyclone formation (just west-northwest of the Republic of Cabo Verde Islands near 17N-27W)