The entire Philly region is under a flash-flood watch for Wednesday

An "isolated tornado" isn't out of the question, the weather service says. Rains won't affect the Danelo Cavalcante search, say state police.

Clouds shroud the Center City skyline after storms passed through Philly in July. Heavy rains are possible on Wednesday, prompting a flood watch.Read moreMonica Herndon / Staff Photographer

by Anthony R. Wood

Published Sept. 12, 2023, 5:19 p.m. ET

Warning of downpours that could disrupt the morning commute and coax some streams out of their banks, the National Weather Service has the entire Philly region under a flash-flood watch from 2 a.m. until 5 p.m. Wednesday.

After weeks of hit-or-miss showers and thunderstorms, these are likely to be of the hit variety, said Paul Fitzsimmons, a lead forecaster at the National Weather Service office in Mount Holly.

“I think pretty much everyone is going to see rain,” he said.

Showers, and possibly thunderstorms, were all but certainties from 2 a.m. until about daybreak, the weather service said, and likely to continue into the afternoon.

With the atmosphere well-energized and juiced with moisture, rains could fall at rates of one to two inches an hour, the weather service said, and some storms could kick off damaging wind gusts. And an “isolated tornado” isn’t out of the question, the weather service said.

Forecasters said the heaviest rains are likely to back off by late morning, although more showers could pop up in the afternoon.

Fitzsimmons said the flood watch extends until 5 p.m. in part because it can take a while for waterways to respond to upstream rains and runoff.

Downpours during the weekend doused parts of Ocean and Camden Counties and Philly, which officially measured nearly two inches on Sunday.

However, overall rain deficits have been building in Philadelphia and its neighboring counties in the last month, according to the Middle Atlantic River Forecast Center, which uses a sampling of measuring stations to compute countywide totals.

Delaware County rainfall has been about 40% of normal; Philadelphia is at 62%; and Gloucester County at 64% through Tuesday. While stream levels are on the low side, that can change rapidly along flood-prone creeks such as the Neshaminy and the Brandywine.

The trigger for the expected rains is an approaching cold front that will leave in its wake a splendid run of sunny days from Thursday through the weekend, with highs in the 75- to 80-degree range and cool nights, conditions that fall foliage experts say are ideal for color intensity.

Hurricane Lee is expected to remain well offshore, its local impact limited to high waves and rip currents at the Shore.

Meanwhile, come thunder or high water on Wednesday, Pennsylvania State Police say the search will continue for fugitive Danelo Cavalcante, the convicted murderer who escaped from the Chester County jail on Aug. 31.

“We’ll keep an eye on anticipated weather conditions,” said state police spokesperson Lt. Adam Reed. But, “our troopers are equipped with proper rain gear to continue the search.”