El Niño is expected to continue to strengthen and go down in the history books as one of the strongest ever, according to the World Meteorological Organization.
The U.N. agency said that a mature and strong El Niño event is contributing to extreme weather patterns, and it is expected to strengthen further by the end of the year.
The Geneva-based organization released its assessment on the eve of an international El Niño conference in New York.
The weather phenomenon has brought drought to Guanacaste and much of the Pacific coast.
Peak three-month average surface water temperatures in the east-central tropical Pacific Ocean will exceed 2 degrees C above normal, placing this El Niño event among the three strongest since 1950, said the agency.
Typically, El Niño events peak late in the calendar year, with maximum strength between October and January of the following year, said the meteorological agency.
They often persist through much of the first quarter of that year before decaying, it added.
Costa Rica is entering its annual dry season now which will magnify the effects of El Niño.
Previous strong El Niños were in 1972 to 73, 1982 to 83 and 1997 to 98.
The naturally occurring El Niño event and human induced climate change may interact and modify each other in ways which scientists have never before experienced, said Michel Jarraud, secretary general of the agency.