Tropical Storm Nicole
No adverse weather is currently expected from Nicole in the next five days. However, Nicole is forecast to take on an erratic track starting Friday, keeping the storm within the ‘potential threat’ radius (400 nm) for at least the next five days while maintaining moderate tropical storm strength.
[Potential Threat: When the center of a tropical cyclone is expected to pass within 400 nm of Bermuda within 72 hours. – BWS Glossary]
Further, the steering patterns that are responsible for Nicole’s erratic forecast track between Friday through Sunday are unstable. That means small changes in the steering pattern will result in large changes in the eventual track of Nicole. Adverse weather related to Nicole will therefore remain a possibility early Saturday, through and beyond Sunday.
Nicole originated from a tropical wave embedded in the inter-tropical convergence zone in the Central Atlantic. The wave tracked northwestward, staying northeast of the Caribbean. It experienced significant vertical wind shear from an upper level low nearby that slowed organization of the cyclone. Yesterday morning, the low became stacked with the axis of the weakening upper level low where vertical wind shear is locally lower, and convection was able to organize allowing a tropical cyclone to form.
On the 12pm forecast from NHC, Nicole will be over sufficiently warm waters and in a regime of gradually increasing wind shear. However, how (un)favorable the upper level winds are depends on the eventual evolution of the steering pattern, which is currently being forecast with lower than normal confidence and therefore, Nicole’s intensity forecast is lower confidence than normal. NHC is forecasting near steady intensity over the next three days, then a slight weakening.
Hurricane Matthew is currently exiting Haiti and Cuba where locally extreme damage was likely done. Matthew is about to begin a 36 hour track through the Bahamas impacting many of these islands with violent winds, life-threatening storm surge and heavy rain related flooding. Florida is then at threat from Matthew as the hurricane exits the Bahamas. Matthew too has an uncertain long-range track, with a small but non-zero chance for impacts in Bermuda.
Over the weekend, Hurricane Matthew rapidly intensified into the Atlantic Basin’s first category five hurricane since Hurricane Felix (2007) as it meandered in the eastern and central Caribbean Sea. Matthew then weakened due to a combination of inner core dynamics and some intermittent dry air entrainment, but remained an extremely dangerous category four hurricane.
At category four strength, Matthew made landfall in southwestern Haiti near Les Anglais on Tuesday morning, crossed the Gulf of Gonaives, and made a second landfall in eastern Cuba near Baracoa. Near the landfall locations, a combination of violent category four strength winds and significant storm surge likely caused locally extreme damage. Heavy rains, spreading far from the center of Matthew, are responsible for flooding across the Caribbean, particularly in Haiti, Cuba, and the Dominican Republic.
Interaction with land over Haiti and Cuba has weakened Matthew only slightly to a category 3 hurricane. Matthew is currently in the south-central Bahamas. Violent winds and storm surge will make conditions extremely dangerous and locally life-threatening on many of the Bahamas islands as Matthew tracks through the island chain.
Further, Matthew is in a moist environment with low vertical wind shear and is over some of the warmest water in the Atlantic, as a result, Matthew is expected to at least maintain its category three intensity, if not re-strengthen as it moves through the Bahamas over the next day or so.
[Category what? See NOAA’s explanation of the Saffir-Simpson Hurricane Wind Scale]
By late on Thursday, Matthew is expected to be approaching the east coast of Florida as a major hurricane. Between day two and three Matthew is expected to parallel the east coast of Florida before turning sharply to the east on Saturday. However, small changes in the track of this hurricane could bring violent winds onshore, or keep them far off shore leading to an unusually wide range of possible impact scenarios despite a forecast with near average confidence through this timeframe.
After the eastward turn on Saturday, as with Nicole, the forecast becomes much less confident. Right now the most supported scenario appears to have Matthew beginning to turn to the south then west and threaten the Bahamas and Florida once again in the 5-10day range. However, Matthew could also continue eastward and become a ‘potential threat’ to Bermuda. At this time, no adverse weather is expected from Matthew in Bermuda.