Rainy weather caused the national emergency commission to emit a warning alert Thursday for the Caribbean and the northern zone where strong winds are accompanied by downpours.
The alert was prompted by information from the Instituto Meteorológico Nacional that confirmed that the high pressure in the Caribbean that was bringing rains to the north and eastern parts of the country.
The weather institute said that 70 millimeters (about 2.75 inches) had fallen in some places during the previous 12 hours and that rivers were rising along the Caribbean coast. The Río Reventazón was reported to be running out of its banks already.
The institute said it expected the rains to continue until Saturday.
The weather system was bringing light rain to the Central Valley and the mountains of Guanacaste, said the institute.
Some downpours were predicted for the Pacific coast.
Wednesday marks the end of the traditional 2011 hurricane season in both oceans. The only current storm is Kenneth in the eastern Pacific, which is moving west and well away from any landfall.
The high pressure in the Caribbean is one reason that the U.S. Hurricane Center in Miami, Florida, says there is little chance of any storms forming there for the next two days.
So far there have been 11 tropical storms and seven hurricanes in the Atlantic. Of the latter, there were two category 4 hurricanes, Katia and Ophelia, and one category 3 hurricane, Irene.
In the Pacific there were 10 hurricanes, one tropical storm and two tropical depressions. Five of the hurricanes were category 4.
México bore the brunt of the storms that made landfall, although some had an effect on Costa Rican weather.