Hurricane Ella, the small but powerful storm chugging toward Cape Hatteras was expected to veer harmlessly out to sea today and pose little threat to the Washington area and shore points in Maryland, National Weather Service forecasters said last night.

A ridge of high pressure over the East Coast should deflect the hurricane and keep it from coming ashore, forecasters said. For Labor Day weekenders, this should mean generally fair and pleasant weather today through Monday in the immediate Washington area.

Along the Delmarva shore, forecasters called for more cloudiness with a chance of drizzle today and tomorrow, but fair and pleasant conditions Monday.

A hurricane watch remained in effect last night, however, for the Outer Banks of North Carolina from Cape Lookout to the Virginia border.

The center of the 200-mile wide Hurricane Ella with winds up to 115 miles an hour, was about 300 miles southeast of Cape Hatteras last night, according to the National Hurricane Center in Miami. The storm system, described by veteran weather service observers as smaller than average, was moving sluggishly in a northwesterly direction and had slowed to 5 miles an hour last night.

"It's a very compact storm," said forecaster Richard Crouthamel. ". . . We're not expecting much effect from it here. Once it hits that (high pressure) ridge, it'll start heading north and then northeast back out into the Atlantic."

"We believe it will just barely miss the Outer Bank (of North Carolina)," said hurricane center forecaster Miles Lawrence. "But it being so close, we felt it necessary to warn residents along the coast." He and other forecasters stressed that coastal areas north of Virginia were in no immediate danger.

While Ella lurked uncertainly in the Atlantic yesterday, Washington area residents began recovering from the hottest and one of the most miserable Augusts on record here.

Unrelenting heat, humidity and 17 days of rain left residents gasping. The temperature for the month averaged 81.3 degrees, the hottest August since the National Weather Service started keeping records here in 1872 and 4.2 degrees above the normal of 77.1 degrees for the month.

It was also the second hottest summer month ever recorded here, exceeded only by July, 1955, which averaged 82.9 degrees, according to weather service records.

As if that weren't enough, storms dumped 5.85 inches of rain on the area, 1.18 inches above normal. Thunderstorms occurred on seven days, and unusually high humidity kept a stranglehold on the area for almost the entire month, according to National Weather Service observer Don Marier.

"After a month like that, things can only get better in September," said forecaster Harold Hess.

Despite the record heat for the month, peak temperatures during the days never exceeded 93 degrees - compared with a high of 100 degrees in July - and the daily high temperature for August averaged 88.7 degrees, only 2.1 degrees warmer than the normal August daily average.

What caused the record heat and extreme discomfort was that it never cooled off at night. The average low temperature for the month was a muggy 73.8 degrees - 6.2 degrees above the normal average low of 67.6 degrees.

From July 30 to Aug. 20, the temperature never dropped below 70 degrees, the longest stretch of such temperatures in weather service records. During the entire 31-day month, the thermometer fell into the 60s on only three nights, on Aug. 21, 22 and 23.

Why didn't it cool off at night? "Two factors," said Marier. "We had quite a bit of southerly (air) flow from the Gulf area bringing in warm temperatures, and we had an unusual amount of cloudiness at night. The cloud cover acted like a greenhouse and wouldn't let the heat escape."

The rain that drenched the area wasn't all bad. The Potomac River is brimming, according to the U.S. Geological Survey, ground water reserves, have been replinished heading off any possibility of a water shortage like that of last summer.

The river flow was clocked at an average of 7.3 gallons a day at Little Falls, nearly four times the normal August flow, according to the survey.

"In fact," said survey hydrologist Myron Lys, "the combineed average flow of about 6.5 billion gallons a day for July and August, 1978 appears to be among the "wettest" of any July-August period since records began in 1930."