UPDATE 1-Houston-Area refineries operate normally as tropical storm moves ashore -sources

(Adds weather forecast, refinery details)

HOUSTON, Sept 17 (Reuters) - Refineries in Houston, Texas City and Sweeny, Texas were operating normally as Tropical Storm Imelda came ashore on Tuesday afternoon, said companies and sources familiar with plant operations.

Eight refineries in the Houston metropolitan area, Texas City and Sweeny can process a combined 2.5 million barrels per day (bpd), or 13.6% of national capacity, of crude oil.

Weather forecasters said as much as one foot (30.5 cm) of rain could fall on Houston on Tuesday night. Area school districts and colleges canceled classes for Wednesday.

Operations were normal on Tuesday at Exxon Mobil Corp's 560,000 bpd refinery and Phillips 66's 265,000 bpd Sweeny refinery, spokesmen for the companies said.

Operations at Royal Dutch Shell Plc's 340,000 bpd Deer Park, Texas, refinery were stable, a spokesman said.

Sources said Marathon Petroleum Corp's 585,000 bpd Galveston Bay Refinery in Texas City was also operating normally after flaring earlier in the day.

Lyondell Basell Industries' 263,776 bpd Houston refinery continued with normal production with no plans to reduce operations, said Gulf Coast market sources.

(Reporting by Erwin Seba, Editing by Rosalba O'Brien)