(Updates with latest advisory predicting Joaquin will become a hurricane)
By David Adams
MIAMI, Sept 29 (Reuters) - Tropical Storm Joaquin strengthened east of the Bahamas and is expected to become a hurricane on Wednesday before making a sharp northerly turn taking it parallel to the U.S. east coast, forecasters said.
The storm is forecast to strengthen over the next few days and could threaten the Carolinas at the weekend as a Category One hurricane with winds reaching 90 mph (145 kph) on the Saffir-Simpson wind intensity scale, according to the National Hurricane Center (NHC).
“Tropical storm conditions could reach portions of the Central Bahamas by Thursday morning,” the NHC said.
Long-range forecast models were highly uncertain as it moves north and it could stay well offshore or brush the Outer Banks, before possibly heading towards the north-east coast, the NHC said.
Heavy rain over the northern Appalachians and New England over the next two to three days could greatly enhance the potential for Joaquin to cause flooding if it comes ashore, forecasters at the privately-run Weather Underground said.
Warm water, which give storms energy, could help the storm intensify rapidly.
As it moves towards the Bahamas “Joaquin will be passing over ocean temperatures near 30°C (86°F)- the warmest seen there since record keeping began in 1880,” according to Jeff Masters and Bob Henson, meteorologists who co-author a blog for Weather Underground.
Joaquin was the tenth named storm of the 2015 Atlantic hurricane season after forming east of the Bahamas late Monday. It was located about 405 miles (650 km) east of the northwestern Bahamas on Tuesday, with maximum sustained winds of 65 mph (100 kph), the Miami-based NHC said.
Joaquin is moving toward the west-southwest at 5 mph (7 kph), the NHC said, with tropical storm force winds extending 90 miles (150 km) from the center, NHC said.
The government’s annual forecast predicted a quieter-than-normal 2015 Atlantic hurricane season, with six to 10 named storms and up to four reaching hurricane status of 74 mph (119 kph).
So far only two hurricanes have formed, Danny and Fred, which both ran out of steam while still far out at sea.
Among the factors in this year’s predicted weaker hurricane season is the El Niño weather phenomenon, the warming of Pacific waters that affects wind circulation patterns and makes the formation of hurricanes in the Atlantic-Caribbean basin less likely. (Reporting by David Adams; Editing by Grant McCool and Chris Reese)