Erin reached tropical storm status at 3.00 pm Wednesday, and the Florida-based Hurricane Center issued a storm watch for much of the state's gulf coast.
At 3.30 pm GMT, Erin's centre was located about 400 kilometres east of Brownsville, Texas, and some 480 kilometres northeast of La Pesca, Mexico.
Erin was moving in a west-northwest direction at about 19 kilometres per hour.
The storm had maximum sustained winds of 65 kilometres per hour, with higher gusts. Forecasters expected it to strengthen over the next 24 hours.
Meanwhile Tropical Storm Dean, which formed in the central Atlantic, gained strength and threatened to become the first hurricane of the 2007 north Atlantic season.
At 3.00 pm GMT Dean was located some 1,685 kilometres east of the Lesser Antilles.
It was moving at around 32 kilometres an hour towards the Caribbean on a path to rip through the islands of Puerto Rico, Hispaniola and Cuba.
The hurricane season normally extends from early June to late November, but US forecasters on August 9 warned that up to nine storms could still develop into hurricanes in the next months.
UPDATE: Tropical Storm Dean
DEAN INTENSIFYING OVER THE CENTRAL TROPICAL ATLANTIC...
A HURRICANE WATCH MAY BE REQUIRED FOR PORTIONS OF THE LESSER
ANTILLES LATER TONIGHT OR EARLY THURSDAY. INTERESTS IN THE LESSER
ANTILLES SHOULD MONITOR THE PROGRESS OF DEAN.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL WEATHER OFFICE.
UPDATE: Hurricane Flossie
A hurricane watch was cancelled for Hawaii's Big Island hours after Hurricane Flossie turned the seas into roiling giant surf.
The Central Pacific Hurricane Center in Honolulu cancelled the hurricane watch as the storm weakened, although a tropical storm warning remained in effect late Wednesday.
At 11pm (1900 AEST Wednesday), Flossie was located about 280 kilometres south-southwest of Hilo and about 450 kilometres south-southeast of Honolulu. It was moving north-northwest at about 16km/h.
The hurricane centre downgraded Flossie to a tropical storm after maximum sustained winds dropped to 112km/hour.UPDATE: Typhoon SEAPAT
Warnings were issued about possible large waves and storm surges along coastal areas and residents of low-lying areas and people living near mountain slopes were also advised about possible flash floods and landslides. Sepat is expected to slam into Taiwan on Thursday as a category 4 typhoon, one level below the maximum strength super typhoon, according to British-based Web site, Tropical Storm Risk (www.tropicalstormrisk.com). Tropical storms in the region gather intensity from the warm ocean waters and frequently develop into typhoons that hit Taiwan, Japan, the Philippines and southern China during a season that lasts from early summer to late autumn.