*******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.**********
...FRIDAY OCTOBER 11 2019 7:53 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.
SUBTROPICAL STORM MELISSA...The offshore non-tropical frontal cyclone south of Massachusetts earlier developed a core of thunderstorms..and more recently has bands of clouds and thunderstorms...from instability of the increasingly cold temperatures of the sharepening upper trough approaching from the eastern US. As a result this system is now Subtropical Storm Melissa. The sharpening of the upper trough has been due to southward cold air transport on the west side of Melissa's circulation...and from amplification of warm deep-layered ridging to the north and west. Coastal interests in Bermuda and eastern US shore should take precautions from sea swells and rip currents if venturing through these areas in the next 24 hours. The worst of the ocean effects will continue to be along the northeastern US coast where a large wind field between the deep-layered ridging and Melissa is blowing towards the shoreline. National Weather Service observations indicate strong to damaging gusty winds persisting over coastal Massachusetts including Nantucket...but have subsided elsewhere as the strongest tangible weather associated with Melissa conslidated toward the offshore core of the circulation when the transition to subtropical occurred today. Likewise flash flooding rainfall potential over land has ended. As Melissa acclerates eastward and then northeastward with the upper trough emerging from the United States...weakening going forward is expected. This is because Melissa is likely to be trapped in the western convergence zone of the upper trough while trying to keep up with its fast northeastward acceleration. Cooler water temperatures at the 48 hour forecast position makes it likely that this system will have lost any acquired subtropical characteristics by that timeframe.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 11)...60 mph maximum sustained wind subtropical storm centered south of Cape Cod Massachusetts at 38.2N-69.8W
IOH 24 Hr Forecast (1800Z Oct 12)...50 mph maximum sustained wind subtropical storm centered at 38N-67W
IOH 48 Hr Forecast (1800Z Oct 13)...40 mph maximum sustained wind non-tropical remnant gale centered south of Newfoundland at 43N-56W
AREA OF INTEREST #1...A broad tropical low pressure with showers and thunderstorms in the southern Caribbean region...including Nicaragua and Honduras...have been persisting under split flow upper divergence between westerlies on the south side of an upper trough axis extending from the large central Atlantic upper vortex...and easterlies on the south side of an upper ridge axis in the northwestern Caribbean Sea and western Atlantic. The aforementioned upper trough is expected to become a small cut-off upper vortex to the east...with the south side of the eastern US upper trough expected to leave behind a cut-off upper vortex to the west. The latent heat release of the thunderstorms in the short-term will likely locally bolster warm core upper ridging whose upper outflow is enhanced by the upper vortices...therefore it appears this disturbed weather is not going away anytime soon. After 48 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 trough supporting the current central Canada frontal cyclone...and another upper trough and surface front at 96 to 120 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 to the north of Honduras and east of Belize. Regardless of tropical cyclone formation...heavy rainfall with flash flooding maybe possible over all the land areas listed in the outlook below.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 12)...0% chance of tropical cyclone formation (east coast of Nicaragua)
IOH 48 Hr Outlook (1800Z Oct 13)...0% chance of tropical cyclone formation (east coast of Nicaragua)
IOH 72 Hr Outlook (1800Z Oct 14)...5% chance of tropical cyclone formation (Nicaragua...Honduras...northwestern Caribbean Sea)
IOH 96 Hr Outlook (1800Z Oct 15)...10% chance of tropical cyclone formation (northwestern Caribbean...western Honduras...and just east of Belize)
IOH 120 Hr Outlook (1800Z Oct 16)...0% chance of tropical cyclone formation (western Yucatan peninsula of southeastern Mexico...northern Guatemala...and eastern Bay of Campeche)
AREA OF INTEREST #2...The National Hurricane Center in its 5-day tropical weather outlook has introduce the active tropical wave currently over western Africa due to the NAVGEM...GFS...Euro...and CMC 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 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 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...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 12)...0% chance of tropical cyclone formation (western Africa near 15W)
IOH 48 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 72 Hr Outlook (1800Z Oct 14)...5% chance of tropical cyclone formation (just east of the Republic of Cabo Verde Islands near 15N-21W)
IOH 96 Hr Outlook (1800Z Oct 15)...5% chance of tropical cyclone formation (over the Republic of Cabo Verde Islands near 16N-24W)
IOH 120 Hr Outlook (1800Z Oct 16)...0% chance of tropical cyclone formation (just west-northwest of the Republic of Cabo Verde Islands near 17N-27W)