WASHINGTON (Reuters) - Overnight thunderstorms peppered the Northeast on Monday and threatened to return with damaging wind gusts and hail as record-breaking heat tightened its grip on the Southern and Central Plains.

Hurricane watchers, meanwhile, kept their focus on a Caribbean storm brewing to the east of the Lesser Antilles that could become Tropical Storm Emily sometime on Monday, meteorologist Mark Mancuso said.

Coastal states could be lashed later in the week if the storm moves into the Gulf of Mexico or the Atlantic, he said.

The National Hurricane Center also reported Monday afternoon that Tropical Storm Eugene in the Eastern Pacific had not yet become a hurricane, as expected later in the day.

After a month of record-breaking sizzle across the United States, no relief was in sight for the Southern and Central Plains, where excessive heat warnings remained in effect, according to the National Weather Service.

"Another heat wave is underway once again," Accuweather forecaster Mary Yoon said, adding that 2,676 high temperature records were smashed or tied last month.

Weather service meteorologists said Oklahoma City; Washington, D.C.; and Wichita Falls, Texas all saw their hottest months on record in July.

Temperatures of 100 degrees or more were recorded on 38 days this year in Oklahoma City, where it rained only two days in July, the weather service office in Norman, Oklahoma, said.

Temperatures were expected to reach 105 to 112 degrees this week in Oklahoma and Texas, exacerbating exceptional drought conditions that have persisted in the region.

The National Drought Mitigation Center said a severe southern drought had devastated the largest area of the United States in over a decade in July, charring pasturelands, drying rivers and laying waste to wildlife and livestock.

It said in a report that some 12 percent of U.S. land was seeing "exceptional drought," the biggest contiguous area to suffer such tough conditions in at least 12 years.


The weather service issued an excessive heat warning Monday for western Tennessee with forecasts for Memphis to reach 100 degrees, said Bobby Boyd, a weather service meteorologist in Nashville.

"Nashville had what may very well be the highest heat index on record," said Boyd, when high temperatures and humidity produced a heat index of 114 during the afternoon of July 11.

Further south, the weather service extended a heat advisory for New Orleans to the end of the week and forecast that the heat index would reach 113 degrees on Tuesday due to low-level moisture hovering over the city.

Louisiana is accustomed to oppressive summer conditions, and while New Orleans is technically under drought conditions it has fared better than neighbors due to local rainfall.

For local mule-drawn carriage tour operators, that helps keep business moving.

"The typical New Orleans weather pattern is, it often rains around midday, and that will take the temperature down 10 to 15 degrees," said James Lauga, owner of Royal Carriages Inc.

Regular rains bring relief when regulations require that mules be brought off the street when it hits 95 degrees. In an average summer, Lauga brings the mules in 15 to 20 times, but he hasn't hit the 15 mark yet this year.

"I'd say this summer is less hot than the last two years," Lauga said.

In the Northeast, rattling thunderstorms gave way to blue skies by morning but were expected to return in much greater intensity later in the day.

Damaging wind gusts to 60 miles per hour are expected to blow from eastern Pennsylvania to New York City and into northern New England, bringing hail and some localized flooding, meteorologist Brian Edwards said.

A severe thunderstorm brought heavy rain across the Minneapolis-St. Paul metro area, flooding some lanes on Interstate 94, knocking down trees and cutting power to about 25,000 Xcel Energy customers.