Hurricane Matthew moved toward Haiti on Monday and the threat to the U.S. increased.  At 5:00 pm. EDT on Monday the center of Hurricane Matthew was located at latitude 16.3°N and longitude 74.7°W which put it about 140 miles (220 km) south of Tiburon, Haiti.  Matthew was moving toward the north at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were wind gusts to 165 m.p.h. (265 km/h).  The minimum surface pressure was 940 mb.

Hurricane Warnings are in effect for Haiti and the Cuban provinces of Guantanamo, Santiago de Cuba, Holguin, Granma and Las Tunas.  Hurricane Warnings are also in effect for the Southeastern Bahamas including the Inaguas, Mayaguana, Acklins, Crooked Island, Long Cay, Ragged Island, and for the Central Bahamas including Long Island, Exuma, Rum Cay, San Salvador and Cat Island.  Hurricane Watches have been issued for the Cuban province of Camaguey and the northwestern Bahamas including the Abacos, Andros Island, Berry Islands, Bimini, Eleuthera, Grand Bahama Island and New Providence, and for the Turks and Caicos.  A Tropical Storm Warning is in effect for Jamaica and the south coast of the Dominican Republic from Barahona to Haiti.  Tropical Storm Watches have been issued for the northern coast of the Dominican Republic from Puerto la Plata to Haiti.

The structure of Hurricane Matthew is well organized.  It has a circular eye with a diameter of 18 miles (29 km).  The eye is surrounded by a ring of strong thunderstorms.  Winds to hurricane force extend out about 40 miles (65 km) from the center of circulation.  Thunderstorms around the eye are generating upper level divergence which is pumping out mass in all directions.  Additional rainbands are rotating around the core of Matthew.

The Hurricane Intensity Index (HII) for Matthew is 28.2.  The Hurricane Size Index (HSI) is 15.1 and the Hurricane Wind Intensity Size Index (HWISI) is 43,3.  These indices suggest that Hurricane Matthew is capable of causing regional significant wind damage to Haiti.  Hurricane Matthew is very similar in size and intensity to what Hurricane Dennis was when Dennis hit northwest Florida in 2005.  Hurricane Matthew is stronger and a little bigger than Hurricane Sandy was when Sandy was over the northwestern Caribbean Sea in 2012.

Hurricane Matthew is moving through a very favorable environment.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is not much vertical wind shear.  Matthew is likely to maintain its intensity as it moves toward Haiti.  If a rainband wraps around the eye, then an eyewall replacement cycle could cause temporary fluctuations in intensity.  The future path of Matthew could have a big impact on the intensity of the hurricane.  If the center of Matthew moves over southwestern Haiti, then the Massif de la Hotte could seriously disrupt the lower levels of the circulation.  Mountains in Massif de la Hotte extend up to 7700 feet (2347 meters).  On the other hand, if the eye and eyewall move just west of Haiti, then the inner core is likely to remain intact.  The water around the Bahamas is very warm and if the core of Hurricane Matthew is reasonably intact when it gets there, Matthew will likely regain its intensity.

Hurricane Matthew is moving around the southwestern end of a subtropical high pressure system, which has allowed the hurricane to move just east of due north.  That general motion is expected to continue for another day or so.  In about 24 hours the subtropical high is expected to strengthen and extend westward.  If the high does strengthen, it will force Hurricane Matthew to move more toward the northwest.  Guidance from numerical models has supported this scenario today.  The northwest motion could take Hurricane Matthew over the Central and Northwestern Bahamas during the middle of the week.  A northwesterly track could bring Hurricane Matthew close to Florida on Thursday and near the Mid-Atlantic Coast on Friday.  Based on guidance from the forecast models, the threat to the U.S. increased significantly on Monday.

Hurricane Matthew has the potential to cause regional significant wind damage to Haiti.  Even if the center moves west of Haiti, Matthew will produce very heavy rain and the potential for devastating flash floods and mudslides exists.  There will also be significant storm surges along the coasts of Haiti, the Dominican Republic and eastern Cuba.