If you live in or are visiting Guanacaste or the Central Valley, the rain is about to switch off. Costa Rica’s dry season settles over the North Pacific and the Central Valley this week, and the rest of the Pacific coast follows within three weeks. That is the outlook from the National Meteorological Institute (IMN), whose four-week forecast goes from Nov. 9 to Dec. 6 and describes the dry season taking hold across the Pacific slope and the Central Valley under a pattern of below-normal rainfall.
With that said, here is the timeline. The North Pacific, which is Guanacaste and the Central Valley, home to San José, Alajuela, Heredia and Cartago, enter the dry season this week. The Central Pacific, including Quepos and Manuel Antonio, follows the week after.
The South Pacific, from Dominical and Uvita down to the Osa Peninsula, joins the week of Nov. 23 to 29. By Nov. 30, the IMN expects very dry conditions across the North Pacific, the Central Pacific and the Central Valley. Keep in mind, dry does not mean zero rain, at least not yet. For this week, the forecast still allows weekly totals of 1 to 70 millimeters (up to 2.8 inches) in the North Pacific and 5 to 80 millimeters (0.2 to 3.1 inches) in the Central Valley, mostly as isolated afternoon showers in the mountains.
The Central Pacific could also see 10 to 80 millimeters (0.4 to 3.1 inches) this week, and the South Pacific 20 to 80 millimeters (0.8 to 3.1 inches). Today is the hand-off. The low-pressure system that soaked the Pacific over the weekend is drifting west, away from the coast. Expect some early rain on the Guanacaste coast this morning, isolated afternoon showers in the mountains and stronger trade winds from the afternoon on but tonight should be dry.
The weekend left its mark first. Nosara recorded 51 millimeters (2 inches) of rain on Sunday, and parts of the eastern Central Valley reached 60 to 65 millimeters (2.4 to 2.6 inches), according to the IMN. That followed a Saturday when five regions were on yellow alert. Those afternoon winds are the real signal. Trade winds are the signature of the dry season in the Central Valley and Guanacaste as they bring cool, clear mornings and blue skies, but they also dry out pastures and forest quickly.
If you are on the Caribbean coast or in the Northern Zone, nothing changes. Those regions have no defined dry season but even so, the IMN expects rainfall there to run about 30 percent below normal from November through January. This year’s switch comes in the middle of a very strong El Niño, which the IMN expects to hold at that intensity through January. The institute has warned that temperatures could run up to 2 degrees Celsius (3.6 degrees Fahrenheit) above normal and may break records, in line with a December El Niño peak forecast by the World Meteorological Organization.
IMN climatologist Daniel Poleo said in October that the transition could be drier than normal, after a month the institute projected would end 40 to 60 percent short of normal rainfall in much of the country. Back in September, forecasters were already saying El Niño could end the rainy season early.
A drier-than-usual start matters most for water availability. Guanacaste enters the dry months after a year in which water rationing reached dozens of Pacific communities and authorities issued the country’s first red alert at sea. One caveat before you put the umbrella away. The hurricane season runs until Nov. 30 in both the Atlantic and the Pacific, and storms during the transition can still bring short, intense downpours. On Sunday, the US National Hurricane Center gave the weekend’s low a 20 percent chance of becoming a tropical depression within 48 hours.
Having said all that, what does this mean for you? Pack a light layer for windy Central Valley mornings, carry more water than you think you need on Pacific beaches, and keep an eye on afternoon clouds in the mountains for the rest of November. For most of Costa Rica, the change means clearer skies, cooler highland nights and long stretches of sunshine through April. It also starts the five-month stretch when every liter of water on the Pacific side counts.
