UPDATE 3-Tropical Storm Nate pounds Central America, heads for U.S.

(Adds state of emergency declared for New Orleans and 29 Florida counties)

SAN JOSE, Oct 5 (Reuters) - Tropical Storm Nate unleashed intense rainfall across much of Central America on Thursday, killing at least 3 in Costa Rica as it heads for the U.S. Gulf Coast where it is expected to strike as a hurricane this weekend.

Nate is expected to strengthen into a Category 1 hurricane by the time it strikes the U.S. Gulf Coast on Sunday, National Hurricane Center (NHC) spokesman Dennis Feltgen said.

Costa Rica's government declared a state of emergency, closing schools and all other non-essential services while emergency officials reported three killed due to the heavy rains, including one child.

Highways were closed due to mudslides and power outages were also reported in parts of Costa Rica, where authorities deployed more than 3,500 soldiers.

In Nicaragua, three people have been reported missing and schools also shut due to the rainfall, which the Miami-based center said could be as much as 30 inches (76 cm) in some isolated areas.

At about 2 p.m. EDT (1800 GMT) on Thursday Nate was about 50 miles (80 km) northwest of Puerto Cabezas, Nicaragua, and about 50 miles (80 km) south-southwest of Puerto Lempira, Honduras, moving northwest at a speed of 9 mph (15 kph), the NHC said.

Nate, which had maximum sustained winds of 40 mph (64 kph), was expected to move across northeastern Nicaragua and eastern Honduras on Thursday and enter the northwestern Caribbean Sea Thursday night.

The storm will be "near hurricane intensity" when it approaches the Yucatan Peninsula late on Friday, the NHC said.

Nate will dump 15 to 20 inches (38 to 51 cm) of rain over Nicaragua, and both Costa Rica and Panama were to get 5 to 10 inches (13 cm to 25 cm) of rain and 20 inches (51 cm) in some isolated areas, the NHC said.

U.S. officials from Florida to Texas told residents on Thursday to prepare for the storm. A state of emergency was declared for 29 Florida counties and the city of New Orleans.

Feltgen said Gulf Coast residents should monitor the storm and prepare supplies, but added it was too early to predict with any certainty where Nate would make landfall.

"The threat of the impact is increasing, so folks along the northern Gulf Coast should be paying attention to this thing," Feltgen said.

Major oil producers including Exxon Mobil Corp, Chevron Corp and Royal Dutch Shell Plc have begun withdrawing personnel from their production platforms in the Gulf of Mexico. (Reporting by Enrique Andres Pretel in San Jose, Oswaldo Rivas in Managua, Elida Moreno in Panama City, Gustavo Palencia in Tegucigalpa, Nelson Renteria in San Salvador, Sofia Menchu in Guatemala City, and Bernie Woodall in Fort Lauderdale, Fla.; Additional reporting by Nallur Sethuraman and Arpan Varghese in Bengaluru; Writing by David Alire Garcia and Bernie Woodall; Editing by Alistair Bell and Sandra Maler)