San José, Costa Rica, since 1956

La Niña to Bring It On

The rainy season will likely start the end of April in much of the Central Valley and Pacific regions, and meteorologists are predicting a nasty one.

But sensational summerlike days this week have analysts at the National Meteorological Institute (IMN) sweating their initial predictions of rainfall arriving a full fortnight earlier than usual.

“The official prediction hasn’t changed but we’re waiting to see what happens this coming week particularly in the Central Valley,” says IMN meteorologist Rosario Alfaro. She says there’s a slight chance the “transition,” a period that ushers sputters of rain in to end the dry season, could continue further, but again, no forecast has yet indicated this.

The rainy season, known in Spanish as estación lluviosa, already began in the southern Pacific earlier this month – leaping straight in with no transition – yet even there the rain has let up a bit this past week, Alfaro said.

The thermometer won’t begin to noticeably show the season change until June, according to Alfaro. But she saif central Pacific Puntarenas, for example, drops from an average maximum temperature of 34.8 degrees Celsius (94.6 degrees Fahrenheit) in April to 31.5 degrees (88.7 degrees F) in October.

Throughout the Pacific and Central Valley showers fell early this year, though daily rainy season precipitation has not begun as soon as weather analysts had previously forecast.

Scattered showers characteristic of the transition have persisted in parts of the Central Valley, but earlier predictions said the full-fledged rainy season was to begin as earlier as April 16. Now meteorologists say it should start next week in the Central Valley, and a bit later in May in the northwest Guanacaste province, said another IMN weatherwoman, Rebeca Morera.

Delays aside, the new season is still up over a week early in some areas, and weather analysts say La Niña is the culprit.

La Niña, El Niño’s cooler sister weather system characterized by cold ocean temperatures in the Equatorial Pacific, affects different parts of Costa Rica differently, with more rain along the Pacific and Central Valley and dryer days on the Caribbean, according to the IMN.

The institute’s April 18 report suggests the phenomenon might be easing up, an assertion that has been concurred by meteorologists in other parts of the world.

Meteorologists, nevertheless, predict a wetter-than-normal 2008 that could see downpours similar to last year’s punishing rainy season. Rain levels may rise as high as 420 centimeters for the year in the southern Pacific – 15% above normal – and 270 centimeters in the northern Pacific – up 30% from the norm.

The report suggests there will be seven tropical storms and six hurricanes, two on the Caribbean side.

Ahead of the rain, regional weather analysts met this week in Nicaragua, also girding for a heavy hurricane and storm season (NT, April 18). The April 21-23 Central America Climate Forum, coinciding on Tuesday with Earth Day, drew experts to harmonize and update their forecasts, and prepare recommendations for disaster prevention.

Costa Rica’s IMN meteorologist Evelyn Quirós said her institute has already notified the National Emergency Commission (CNE) to be on alert for possible weather damage.

But emergency workers are still fixing the levees, roads, bridges and homes damaged by last green season’s floods (TT, Oct. 19). The commission has made progress, including 1,500 kilometers of fixed roads in 280 communities across the country, according to CNE spokeswoman Rebeca Madrigal.

The commission began in March to organize flood simulations to practice evacuation procedure, according to CNE spokesman Reynaldo Carballo.


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