Hurricane Erin passed south of Cape Cod on Thursday afternoon.  At 5:00 p.m. EDT on Thursday the center of Hurricane Erin was located at latitude 36.4°N and longitude 69.1°W which put the center about 320 miles (520 km) south of Nantucket Island.   Erin was moving toward the northeast at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).   The minimum surface pressure was 952 mb.

A Tropical Storm Warning is in effect for the portion of the coast from Duck, North Carolina to Chincoteague, Virginia.

A Storm Surge Warning is in effect for the portion of the coast from Cape Lookout to Duck, North Carolina.

A Tropical Storm Warning is in effect for Bermuda.

Hurricane Erin started to weaken slowly as it moved over the Atlantic Ocean between Cape Cod and Bermuda on Thursday.  No eye was visible at the center of Erin’s circulation on satellite images.  Bands of showers and thunderstorms were revolving around the center of Hurricane Erin.  Storms near the center of Erin were still generating upper level divergence that pumped mass away from the hurricane.  The removal of mass in the upper levels of the atmosphere almost matched the inflow of mass in the lower levels.  There was slightly more mass flowing into the center of Erin’s circulation.  So, the surface pressure was slowly increasing.

The circulation around Hurricane Erin was very large.  Winds to hurricane force extend out 100 miles (160 km) from the center of Erin’s circulation.  Winds to tropical storm force extend out 320 miles (520 km) from the center of Hurricane Erin.

The Hurricane Intensity Index (HII) for Hurricane Erin is 16.5.  The Hurricane Size Index (HSI) is 36.9 and the Hurricane Wind Intensity Size Index (HWISI) is 53.4.  Hurricane Erin is similar in size and intensity to Hurricane Ike when Ike hit Texas in 2008.  Erin is not quite as strong as Ike was, but Hurricane Erin is bigger than Hurricane Ike was.

Hurricane Erin will move through an environment that will be unfavorable for intensification of a hurricane during the next 24 hours.  Erin will move over water where the Sea Surface Temperatures are near 26°C.  It will move under the eastern side of an upper level trough over the Northeast U.S. and the Great Lakes.  The upper level trough will produce southwesterly winds that will blow toward the top of Erin’s circulation.  Those winds will cause moderate vertical wind shear.  Hurricane Erin will weaken slowly during the next 24 hours.  Erin is likely to make a transition to a strong extratropical cyclone during the weekend.

The upper level trough over the Northeast U.S. and the Great Lakes will steer Hurricane Erin toward the east-northeast during the next 24 hours.  On its anticipated track, the center of Hurricane Erin will pass south of Nova Scotia on Friday.

The large circulation around Hurricane Erin will continue to produce large waves that will move toward the east coast of the U.S.  Erin could continue to cause a storm surge of up to four feet (one meter) along the Outer Banks of North Carolina on Thursday night.  Mandatory evacuations are in effect for Hatteras Island and Ocracoke Island.  Water has already washed over parts of Hatteras Island.  The large waves are likely to cause significant beach erosion.  Conditions along the Outer Banks should start to improve on Friday when Hurricane Erin moves farther away.

The large circulation around Hurricane Erin could also produce tropical storm force winds in Bermuda.