The potential risk posed by Tropical Storm Erin prompted the issuance of Tropical Storm Watches for the Northern Leeward Islands on Thursday afternoon.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Erin was located at latitude 16.7°N and longitude 51.2°W which put the center about 790 miles (1270 km) east of the Northern Leeward Islands.  Erin was moving toward the west at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 998 mb.

Tropical Storm Watches are in effect for Anguilla, Barbuda, St. Martin, St. Barthelemy, Saba, St. Eustatius, and Sint Maarten.

Tropical Storm Erin continued to strengthen gradually on Thursday.  Even though Tropical Storm Erin was strengthening, the distribution of thunderstorms was asymmetrical.  Thunderstorms were occurring mainly in bands in the western side of Erin’s circulation.  Bands in the eastern side of Tropical Storm Erin consisted primarily of showers and lower clouds.  Storms near the center of Erin generated upper level divergence that pumped mass away to the west of the tropical storm.  The removal of mass caused the surface pressure to decrease slowly.

The circulation around Tropical Storm Erin is small,  Winds to tropical storm force extend out 60 miles (95 km) from the center of Erin’s circulation.

Tropical Storm Erin will move through an environment mostly favorable for intensification during the next 24 hours.  Erin will move over water where the Sea Surface Temperatures are near 28°C.  It will move under the southern part of an upper level ridge over the eastern Atlantic Ocean.  The upper level ridge will produce easterly winds that will blow toward the top of Erin’s circulation.  The winds in the lower levels of the atmosphere will also blow from the east, but winds will be stronger in the upper troposphere.  So, there will be some vertical wind shear.  The vertical wind shear will inhibit intensification, but the shear will not be enough to prevent intensification.  Tropical Storm Erin will intensity during the next 24 hours.  Erin is likely to strengthen to a hurricane on Friday.

Tropical Storm Erin will move around the southern side of a high pressure system over the eastern Atlantic Ocean.  The high pressure system will steer Erin toward the west during the next 24 hours.  On its anticipated track, Tropical Storm Erin will move toward the Northern Leeward Islands.  Erin could approach the Northern Leeward Islands on Friday night.

Tropical Storm Erin is likely to bring gusty winds and locally heavy rain to the Northern Leeward Islands.  Heavy rain could cause flash floods in some locations.