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Very Dangerous Hurricane Irma Reaches Cat. 5

Very dangerous Hurricane Irma reached category 5 on the Saffir-Simpson Scale on Tuesday morning.  At 11:00 a.m. EDT on Tuesday the center of Hurricane Irma was located at latitude 12.3°N and longitude 39.1°W which put it about 225 miles (365 km) east of Antigua.  Irma was moving toward the west at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 180 m.p.h. (285 km/h) and there were wind gusts to 210 m.p.h. (340 km/h).  The minimum surface pressure was 931 mb.

Hurricane Warnings are in effect for Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, Sint Maarten, St. Martin, St. Barthelemy, the British Virgin Islands, the U.S. Virgin Islands, Puerto Rico, Vieques and Culebra.  Tropical Storm Warnings are in effect for Guadeloupe and Dominica.  Hurricane Watches are in effect for Guadeloupe, the southeastern Bahamas including the Acklins, Crooked Islands, Long Cay, the Inaguas, Mayaguana, and the Ragged Islands.  A Hurricane Watch is also in effect for the portion of the the coast from Cabo Engano, Dominican Republic to Le Mole St. Nicholas, Haiti.  Tropical Storm Watches are in effect for the portion of the coast from Le Mole St. Nicholas to Port Au Prince, Haiti and from Cabo Engano to Isla Saona, Dominican Republic.

Hurricane Irma intensified rapidly after the completion of the most recent eyewall replacement cycle.  The structure evolved in a large classic Cape Verde hurricane.  The is a large circular eye at the center of circulation.  A ring of very strong thunderstorms surrounds the eye and the strongest winds are occurring in that ring.  Bands of showers and thunderstorms are revolving around the core of Hurricane Irma.  Winds to hurricane force extend out about 60 miles (95 km) from the center of circulation.  Winds to tropical storm force extend out about 160 miles (260 km) from the center.

The Hurricane Intensity Index (HII) for Irma is 44.1.  The Hurricane Size Index (HSI) is 19.8 and the Hurricane Wind Intensity Size Index (HWISI) is 63.9.  Hurricane Irma is as strong as Hurricane Rita was in 2005, but Irma is just slightly smaller than Rita was.  Hurricane Irma is capable of causing widespread catastrophic damage.

Hurricane Irma is moving through an environment that is very favorable for hurricanes.  Irma is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma will likely remain very strong as long as it stays over water.  Additional eyewall replacement cycles could occur and they would result in fluctuations in the intensity of Hurricane Irma.

Hurricane Irma is being steered to the west by a very strong subtropical high over the Atlantic Ocean.  Irma is expected to turn a little more toward the west-northwest as it moves closer to the western end of the high.  On its anticipated track Hurricane Irma will move across the northern Leeward Islands during the next 24 hours.  It will be near Puerto Rico on Wednesday and near the Dominican Republic on Thursday.

Hurricane Irma is an very dangerous hurricane.  It is capable of producing widespread catastrophic damage.  Hurricane Irma will also drop extremely heavy rain and flooding is very possible.

Hurricane Irma Strengthens to Cat. 4, Watch in effect for Puerto Rico

Hurricane Irma strengthened to Category 4 on the Saffir-Simpson Scale on Monday and a Hurricane Watch was issued for Puerto Rico and the U.S. Virgin Islands.  At 5:00 p.m. EDT on Monday the center of Hurricane Irma was located at latitude 16.7°N and longitude 54.4°W which put it about 490 miles (790 km) east of the Leeward Islands.  Irma was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 944 mb.

Hurricane Warnings are in effect for Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, St. Maarten, St. Martin, and St. Barthelemy.  Hurricane Watches are in effect for Guadeloupe, the British Virgin Islands, the U.S. Virgin Islands, Puerto Rico, Vieques and Culebra.  A Tropical Storm Warning is in effect for Guadeloupe.  A Tropical Storm Watch is in effect for Dominica.

The circulation of Hurricane Irma has been going through a series of eyewall replacement cycles.  A plane flying through Irma reported concentric eyewalls earlier today.  The two eyewalls appear to have merged.  A small circular eye is at the center of circulation.  A ring of strong thunderstorms surrounds the eye and the strongest winds are occurring in that ring of storms.  Additional bands of showers and thunderstorms are revolving around the core of Hurricane Irma.  Storms around the center are generating strong upper level divergence which is pumping away mass in all directions from the hurricane.

Hurricane Irma has been increasing in size.  Winds to hurricane force extend out about 40 miles (65 km) from the center of circulation.  Winds to tropical storm force extend out about 140 miles (225 km) from the center.  The Hurricane Intensity Index (HII) for Hurricane Irma is 25.1.  The Hurricane Size Index (HSI) is 13.6.  The Hurricane Wind Intensity Size index (HWISI) is 38.7.

Hurricane Irma will move through an environment very favorable for tropical cyclones.  Irma will move over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma could strengthen further and it has a chance to reach Category 5 on the Saffir-Simpson Scale.  Hurricane Irma is likely to go through additional eyewall replacement cycles, which will cause fluctuations in its intensity, but Irma should remain a strong hurricane as it nears the northern Leeward Islands.

The subtropical high pressure system over the Atlantic Ocean has been steering Hurricane Irma toward the west and that general motion is expected to continue for another 12 to 24 hours.  After that time Irma is expected to turn more toward the west-northwest.  On its anticipated track Hurricane Irma will approach the northern Leeward Islands late on Tuesday.  Hurricane Irma could approach Puerto Rico on Wednesday.

Hurricane Irma Moves Toward Leeward Islands, Watches Issued

Hurricane Irma moved toward the northern Leeward Islands on Sunday and Hurricane Watches were issued for a number of those islands.  At 11:00 p.m. EDT on Sunday the center of Hurricane Irma was located at latitude 17.2°N and longitude 51.0°W which put it about 710 miles (1145 km) east of the Leeward Islands.  Irma was moving toward the west-southwest at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 140 m.p.h. (225 km/h).  The minimum surface pressure was 961 mb.

Hurricane Watches were in effect for Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, St. Maarten, St, Martin, and St. Barthelemy.

The circulation of Hurricane Irma is very well organized.  There is a nearly circular eye with a diameter of 30 miles (48 km) at the center of circulation.  The eye is surrounded by a ring of strong thunderstorms and the strongest winds are occurring in the northeastern part of the ring.  Bands of showers and thunderstorms are revolving around the core of Hurricane Irma.  Thunderstorms around the core are generating strong upper level divergence which is pumping mass away in all directions from the hurricane.  Winds to hurricane force extend out about 35 miles (55 km) from the center.  Winds to tropical storm force extend out about 140 miles (225 km) from the center.

The Hurricane Intensity Index (HII) for Hurricane Irma is 20.6.  The Hurricane Size Index (HSI) is 11.7 and the Hurricane Wind Intensity Size Index (HWISI) is 32.3.

Hurricane Irma will move through an environment favorable for intensification.  Irma will move over water where the Sea Surface Temperature is near 29°C and there is warmer water farther west.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma could intensify into a Category 4 hurricane on the Saffir-Simpson Scale.  There is a possibility that Irma could strengthen to Category 5 when it passes near the northern Leeward Islands and moves toward the Bahamas.  Hurricane Irma has already completed several eyewall replacement cycles and there could be more.  Each eyewall replacement cycle could result in fluctuations in the intensity of Hurricane Irma.

A strong subtropical high pressure system over the Atlantic Ocean is steering Hurricane Irma toward the west-southwest.  The high is forecast to weaken just a bit during the next several days and Hurricane Irma is expected to move more toward the west-northwest.  On its anticipated track Hurricane Irma will approach the northward Leeward Islands on Tuesday night.  It will be a strong, dangerous hurricane at that time.

Tropical Storm Emily Makes Landfall on West Coast of Florida

Tropical Storm Emily made landfall on the west coast of Florida at Anna Maria Island late Monday morning.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Emily was located at latitude 27.5°N and longitude 82.7°W which put it about 10 miles (15 km) northwest of Bradenton, Florida.  Emily was moving toward the east at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1005 mb.  A Tropical Storm Warning was in effect for the portion of the coast from Anclote River to Bonita Beach, Florida.

Thunderstorms developed near the center of the non-tropical low pressure system over the eastern Gulf of Mexico.  Latent energy released higher in the atmosphere by condensation in those storms created a warm core and the low pressure system made a transition to Tropical Storm Emily.  Thunderstorms near the core of Emily were generating a small area of upper level divergence.  Thunderstorms near the core, a warm core and upper level divergence are part of the typical structure of a tropical cyclone, which is why the National Hurricane Center classified the system as Tropical Storm Emily.  Emily has a well developed circulation, but most of the bands of showers and thunderstorms are in the eastern half of the tropical storm.  Drier air northwest of Emily and vertical wind shear are the probable causes of the asymmetrical distribution of precipitation.

Tropical Storm Emily is bringing gusty winds and heavy rain to parts of Central Florida.  A surface weather station in Sarasota (KSRQ) reported a sustained wind of 39 m.p.h. (63 km/h) and a wind gust of 49 m.p.h. (80 km/h).  The Skyway Bridge over Tampa Bay was closed due to strong winds.

Tropical Storm Emily is likely to weaken as it moves eastward across Central Florida.  When Emily moves over the Atlantic Ocean, it will move over water where the Sea Surface Temperature is near 29°C.  Emily could strengthen back into a tropical storm at that time.

Emily is being steered toward the east by a high pressure system north of the tropical storm.  An upper level trough over the Midwestern U.S. is forecast to move southeastward.  When Emily reaches the Atlantic Ocean southwesterly winds ahead of the trough will turn the tropical storm toward the northeast.

Non-Tropical Low Forms Over Northeast Gulf of Mexico

A non-tropical low pressure system formed over the northeastern Gulf of Mexico on Sunday.  The low pressure system is currently designated as Invest 98L.  At 2:00 p.m. EDT on Sunday the center of Invest 98L was located at latitude 28.4°N and longitude 85.5°W which put it about 100 miles (160 km) south-southwest of Apalachicola, Florida.  It was moving toward the east at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1009 mb.

The low pressure system formed along a frontal boundary that stalled over the northeastern Gulf of Mexico.  It is not usual for low pressure systems to form along stationary fronts.  A source of positive vorticity to provide counterclockwise rotation and upper level divergence to pump away mass and allow the surface pressure to decrease will generate a surface low.  The low pressure system does not have a warm core in the middle and upper levels and it is still associated with a frontal system.  So, it is classified as a non-tropical low pressure system.

The low pressure system will be moving through an environment that will be only marginally favorable for a transition to a tropical or subtropical cyclone.  The Sea Surface Temperature in the northeastern Gulf of Mexico is near 30°C.  So, there is plenty of energy to support the formation of a tropical cyclone.  However, an upper level ridge over the central U.S. and a trough over the northeastern U.S. are combining to produce northerly winds of 40 m.p.h. (65 km/h) over the northeastern Gulf of Mexico.  Those winds are generating significant vertical wind shear.  The shear has limited the development of thunderstorms in the northern half of the low and it may be tilting the vertical structure of the low toward the south.  The strong upper level winds will also inhibit divergence on the northern side of the low and they could make it difficult for a warm core to develop in the middle and upper levels.  The air north of the frontal boundary is drier continental air, which is another a negative factor for transition to a tropical cyclone.  Based on all of the environmental factors the National Hurricane Center is indicating that there is a 30% chance the low could make a transition to a tropical or subtropical cyclone.

The low pressure system is moving a little to the south of due east.  A strong surface high pressure system over the eastern U.S. is now pushing the front toward the south as a cold front.  The low is moving slowly eastward along the front.  Combination of the southward motion of the front and eastward motion of the low produces a forecast motion of a little south of due east.  On its anticipated track the low pressure system could reach the west coast of Florida in 24 to 36 hours.  So, the low has about a day, if it is going to transition to a tropical cyclone over the Gulf of Mexico.

Tropical Depression Cindy Brings Stormy Weather to Southern U.S.

Tropical Depression Cindy brought stormy weather to parts of the southern U.S. on Thursday.  At 11:00 p.m. EDT on Thursday the center of Tropical Depression Cindy was located at latitude 33.1°N and 93.5°W which put it about 70 miles (115 km) southwest of Little Rock, Arkansas.  Cindy was moving toward the north-northeast at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 20 m.p.h. (30 km/h) and there were wind gusts to 30 m.p.h. (50 km/h).  The minimum surface pressure was 1000 mb.

Tropical Storm Cindy made landfall early on Thursday morning near the border between Texas and Louisiana.  Cindy moved steadily northward during the day and it was centered over southwestern Arkansas by Thursday night.  Broad counterclockwise rotation around Cindy transported warm and very humid air over the southern U.S.  Bands of showers and thunderstorms dropped locally heavy rain in some places.  Rivers and streams were above flood stage in several southern states.  Flash Flood Warnings and Flash Flood Watches were issued for portions of the southern U.S. and Ohio River Valley.  Several tornadoes formed in the bands of thunderstorms.  A tornado in Alabama caused property damage.  Southerly winds blowing toward the shore were still causing storm surges along the northern coast of the Gulf of Mexico.

Tropical Depression Cindy is forecast to move northeast toward the Ohio River Valley on Friday.  It will continue to produce locally heavy rain.  A slow moving cold front will approach the region from the west.  A band of stronger convergence could develop where the counterclockwise flow around Cindy interacts with the flow along the cold front.  Higher rainfall totals may occur where this interaction happens.  Wind shear created by the interacting weather systems could also create the potential for some tornadoes.  Tropical Depression Cindy could merge with the cold front during Friday night or Saturday.

Tropical Storm Cindy Nears Northwest Gulf Coast

Tropical Storm Cindy neared the northwestern coast of the Gulf of Mexico on Wednesday evening.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Cindy was located at latitude 28.6°N and longitude 93.4°W which put it about 95 miles (150 km) south-southeast of Port Arthur, Texas.  Cindy was moving toward the north-northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 992 mb.

A Tropical Storm Warning is in effect for the portion of the coast from San Luis Pass, Texas to Grand Isle, Louisiana.

Tropical Cyclone Cindy exhibits a hybrid structure in which a broad surface low pressure system is interacting with an upper low centered near the Upper Texas coast.  There is a distinct center of low pressure at the surface.  A band of showers and thunderstorms is northwest of the surface center.  Drier air in the middle and upper levels wraps around the southern and eastern sides of the center and there are no thunderstorms in those quadrants of the core of Tropical Storm Cindy.  A broad flow of moisture is producing bands of showers and thunderstorms in the outer portions of the eastern and northern sides of the circulation.

Tropical Storm Cindy is moving around the western end of a subtropical high pressure system centered over the Atlantic Ocean.  The subtropical high is steering Cindy toward the north-northwest.  On its anticipated track Tropical Storm Cindy will make landfall near the border between Texas and Louisiana on Thursday.  Cindy will turn toward the north and then the tropical storm will move northeastward on Friday.

Some locations will experience prolonged periods of rainfall and fresh water flooding will be possible in those area.  There could also be a storm surge of 3 to 6 feet (1 to 3 meters) near where the center makes landfall.  A few tornadoes could be spun up as rainbands move over the coast.

Hurricane Matthew Causing Serious Flooding in the Carolinas

Hurricane Matthew produced heavy rainfall which led to serious flooding in South Carolina and North Carolina on Saturday.  The total rainfall in some locations exceeded 10 inches (25 cm) in numerous locations in those two states.  Heavy prolonged rain caused creeks and rivers to rapidly rise and flood.

The National Hurricane Center (NHC) still classified Hurricane Matthew as a hurricane in its 11:00 p.m. EDT advisory.  At 11:00 p.m. EDT on the center of Hurricane Matthew was located at latitude 34.1°N and longitude 76.5°W which put it about 35 miles (55 km) south of Cape Lookout, North Carolina.  Matthew was moving toward the east-northeast at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 982 mb.

A Hurricane Warning is in effect for the portion of the coast from Little River Inlet to Surf City, North Carolina.  A Hurricane Watch has been issued for the portion of the coast from Surf City to Duck, North Carolina including Pamlico and Albemarle Sounds.  A Tropical Storm Warning is in effect for the portion of the coast from Surf City to Duck, North Carolina including Pamlico and Albemarle Sounds.

According to NHC the center of Hurricane Matthew made an official landfall near Cape Romain southeast of McClellanville, South Carolina at 11:00 a.m. EDT on Saturday.  Since that time the center of Hurricane Matthew has moved back out over the Atlantic Ocean.  New bands of showers are forming closer to the center south of the coast of North Carolina.  The winds to hurricane force are occurring over a small area on the southwestern side of Hurricane Matthew.

Easterly winds blowing around the north side of Hurricane Matthew converged with northerly winds blowing along a cold front to generate a broad area of rising motion.  The rising motion and the existing rainbands of the hurricane combined to produce very heavy rain over South Carolina and the southeastern half of North Carolina.  The area of heavy rain spread into southeastern Virginia around Norfolk on Saturday night.  The prolonged heavy rainfall caused the water in creeks and rivers to rise very quickly.  Serious flooding was occurring in parts of South Carolina and North Carolina.  Numerous roads were closed because of flooding in those two states.

Along the coast of North Carolina southeasterly winds were blowing water toward the coast and Hurricane Matthew was still generating storm surges.  When Matthew moves east of the Outer Banks of North Carolina, the wind will change direction and it will blow from the northwest.  Those northwesterly winds will push water in Pamlico and Albemarle Sounds onto the western sides of the Outer Banks.  Storms surges caused by Hurricane Matthew caused varying amounts of damage from Florida to North Carolina.  The most destructive storm surges appear to have been near Jacksonville Beach, Florida, around the barrier islands of Georgia and South Carolina.  However, a full damage assessment has not been made of those locations at this time.

Even though the center of Hurricane Matthew stayed over the Atlantic Ocean most of the time, gusty winds caused power outages from Florida to North Carolina.  As the heavy rain saturated the ground, gusts of winds toppled trees which fell onto power lines.  More power outages are likely in eastern North Carolina and southeastern Virginia as more trees are uprooted.

Hurricane Matthew will slowly move out to sea on Sunday.  Matthew appears to be making a transition to an extratropical cyclone.  During that transition the wind field is likely to expand.  So, conditions should improve slowly over North Carolina and Virginia on Sunday.

Hurricane Matthew Bringing Wind and Heavy Rain to the Carolinas

Hurricane Matthew was bringing wind and heavy rain to South Carolina and North Carolina on Saturday morning after causing damage along the coasts of Florida and Georgia on Friday.  At 9:00 a.m. EDT on Saturday the center of Hurricane Matthew was located at latitude 32.6°N and longitude 79.7°W which put it about 30 miles (50 km) southeast of Charleston, South Carolina.  Matthew was moving toward the northeast at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 963 mb.

A Hurricane Warning is in effect for the portion of the coast from Altamaha Sound, Georgia to Surf City, North Carolina.  A Hurricane Watch is in effect for the portion of the coast from Surf City to Cape Lookout, North Carolina.  A Tropical Storm Warning is in effect for the portion of the coast from Surf City to Duck, North Carolina.

The center of Hurricane Matthew is moving just south of the coast of South Carolina.  The winds to hurricane force are occurring in a small area over the Atlantic ocean near the center of Matthew.  Wind gusts to near hurricane force were occurring occasionally at the coast.  Beaufort, South Carolina reported a wind gust to 71 m.p.h. (114 km/h).  Earlier on Saturday a pier at Foley Beach, South Carolina reported a wind gust to 76 m.p.h. (122 km/h).  Inland stations in South Carolina and North Carolina were reporting winds in the range of 20 to 50 m.p.h. (30 to 80 km) with occasional higher gusts.

The wind damage caused by Hurricane Matthew is likely to be minor in many locations.  The winds are strong enough to bring down trees and cause widespread power outages.  There are also some stronger thunderstorms in some of the rainbands that are capable of causing more severe local wind damage and could spin up brief tornadoes.  Hurricane Matthew is also producing heavy rain over South Carolina and North Carolina.  The relatively slow movement of Hurricane Matthew could produce prolonged periods of heavy rain and cause fresh water flooding.  In addition, southeasterly winds on the east side of Hurricane Matthew are pushing water toward the shore and are causing storm surges at the coast.

An upper level trough over the eastern U.S. is steering Hurricane Matthew toward the northeast and that general motion will continue to today.  On its anticipated track the center of Hurricane Matthew will move very near the coast of South Carolina and North Carolina.  Since about half of the circulation of Hurricane Matthew is over land, friction will cause the hurricane to weaken slowly.

Hurricane Matthew Brings Wind, Rain and Surge to Northeast Florida

Hurricane Matthew brought gusty winds, heavy rain and storm surges to northeast Florida as the center of the hurricane moved northward just east of Florida on Friday.  A weather station on the tip of Cape Canaveral reported a wind gust to 107 m.p.h. (170 km/h) when the western side of the eyewall moved over that location.  Wind gusts to 71 m.p.h. (115 km/h) were reported at Daytona Beach.  A wind gust to 86 m.p.h. (139 km/h) was reported by a C-MAN station in St. Augustine, Florida.  Some wind damage and numerous power outages were reported in conjunction with the strong winds.  Easterly winds pushing water toward the coast were generating storms surges along the coast.

At 5:00 p.m. EDT on Friday the center of Hurricane Matthew was located at latitude 30.2°N and longitude 80.7°W which put it about 40 miles (65 km) east of Jacksonville Beach, Florida and about 135 miles (215 km) south of Savannah, Georgia.  Matthew was moving toward the north at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were wind gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 948 mb.  Hurricane Matthew was a Category 2 hurricane on the Saffir-Simpson Scale.

A Hurricane Warning is in effect for the portion of the coast from the Flagler/Volusia County line in Florida to Surf City, North Carolina.  A Tropical Storm Warning is in effect for the portion of the coast from Surf City to Duck, North Carolina including Pamlico and Albemarle Sounds.  A Tropical Storm Warning is also in effect for the portion of the coast from the Brevard/Volusia County lie to the Volusia/Flagler County line in Florida.

The eye and the core of Hurricane Matthew remained over the Atlantic Ocean as Matthew moved parallel to the east coast of Florida.  Occasionally, the western side of the eyewall would move over the coast and bring stronger winds to those areas.  The remnants of the smaller inner eyewall dissipated during the afternoon.  Once the eyewall cycle was completed the remaining outer eyewall began to contract.  Thunderstorms around the eye generated enough upper level divergence to pump out mass and limited the increase of the surface pressure.  As a result, a strong pressure gradient force is still producing winds of over 100 m.p.h. (160 km/h) in the north and northeastern parts of the eyewall.

Hurricane Matthew has been moving around the western end of a subtropical high pressure system which steered the hurricane toward the north on Friday.  An upper level trough over the Central U.S. will move east and southwesterly winds with the trough will start to steer Matthew toward the northeast later tonight.  It is not clear exactly when the turn will occur and the exact timing of the turn to the northeast is very important.  If Hurricane Matthew continues to move north, the northern eyewall which contains the strongest winds could reach Savannah and the coast of South Carolina in 6-10 hours.  If those winds reach the coast, then the damage will be more severe.  If Hurricane Matthew turns northeast before the northern eyewall reaches the coast, then the damage will be less.

Even though Hurricane Matthew weakened slightly to a Category 2 hurricane and is no longer officially a major hurricane, it is still capable of causing regional serious damage.  Matthew will cause wind damage and widespread power outages along the coasts of Georgia and South Carolina, even if the center of the eye does not officially make landfall.  If the center of the eye brings the northern eyewall over the coast, the winds will be much stronger and the damage will be greater.  In addition, easterly winds on the northern side of Hurricane Matthew will drive water toward the coast and create serious storm surges.  In places where the shape of the coast funnels water into smaller areas, the surges will be even more dangerous.