Track forecast for Tropical Storm Bonnie. (National Hurricane Center)

8:28 a.m. Sunday update: Bonnie has weakened from a tropical storm into a tropical depression as it pushes toward the Georgia and Carolina coastlines, the Associated Press reported.

(This article, originally published midday Saturday, has been updated.)

There’s never a good time for a tropical storm, even a weak one. But most would agree Memorial Day weekend is particularly bad timing, especially those along the South Carolina coast, where a tropical storm warning is in effect ahead of heavy rain, somewhat strong winds, and a possible 1- to 2-foot storm surge.

Tropical Storm Bonnie was downgraded to a tropical depression before making landfall in South Carolina Sunday morning, May 29. It's the first storm of the year to threaten the U.S. (Reuters)

Bonnie, the season’s second named storm, achieved tropical storm status late this afternoon. It is currently centered in the Atlantic Ocean about 135 miles south-southeast of Charleston, S.C. Maximum sustained winds of 40 mph have increased modestly since yesterday. Slight strengthening is possible overnight before gradual weakening on Sunday.


Satellite view of Tropical Storm Bonnie Saturday evening. (NOAA)

The storm is forecast to make landfall near Charleston, S.C. Sunday morning or afternoon. Heavy rains have already begun falling near the coast and moved towards South Carolina’s interior.

Because this is a relatively weak tropical storm, rain rather than wind or storm surge is considered the greatest hazard. That said, sustained winds over 30 mph are like along the South Carolina coast tonight, with the National Hurricane Center showing a 40 to 50 percent chance of tropical storm force winds (sustained at 39 mph or higher).

The system’s circulation, along with occasional showers and thunderstorms, may linger for several days along the South Carolina-North Carolina coast, gradually weakening through midweek.

The rain is expected to be heaviest in South Carolina overnight, before spreading northward into North Carolina and Virginia Sunday. Generally the storm is forecast to produce 1 to 3 inches of rain near its core, with locally up to 5 inches.

Northern Virginia, the District, Maryland and Delaware get in on the rain late Sunday afternoon into Monday, with up to about 1 to 2 inches possible in many spots as tropical moisture surges northward far from the core of the system.


Rainfall forecast through 8 p.m. Monday night. (NWS)

D.C. area impacts

In the D.C. area, moisture streaming out ahead of the system brings a slight (20-30 percent) chance of showers Sunday afternoon. But most of the rain probably holds off until evening (starting between 5 and 10 p.m. from southwest to northeast), keeping much of the daylight hours dry.

The period of heaviest rain is likely to occur between Sunday night after dark and early Memorial Day.

The band of heaviest rainfall, which could be generally up to about 2 inches with locally higher amounts, could be narrow and is thus hard to pinpoint. Below are model rainfall amount forecasts.

The GFS model shows the band of heaviest rain (1 to 3 inches) just west of D.C. and Interstate 95, with lighter amounts to the east …


GFS total rainfall forecast through Monday morning. (StormVistaWxModels.com)

The European model suggests 1 to 2 inches of rain across the area through Monday afternoon, with a tendency for the heaviest rainfall along and east of I-95 …


Rainfall forecast by European model between Sunday and Monday night. (StormVistaWxModels.com)

The NAM model shows lighter amounts for the D.C. area, generally 0.25 to 0.75 inches, with 1 to 3 inches+ totals confined to lower Southern Maryland and parts of eastern Virginia …


NAM total rainfall forecast through Monday afternoon. (StormVistaWxModels.com)

While a chance of showers may linger through the day on Monday, it now seems likely that the steady soaking rain exits the area by mid- to late-morning. So don’t cancel that Memorial Day barbecue quite yet. Although rain probably continues later in the day at the beaches.

For more forecast details, see our latest D.C. area forecast through the holiday weekend and into next week.