In late November and early December starts coming a nice breeze from the north bringing with it an invigorating coolness. It's on some nights in December and the first two weeks in January that you might want to use a thicker or extra blanket especially if you live in the higher mountain areas.
Since April is the warmest month of the year and the end of summer or dry season, you can expect the typical daily temperatures to be rather high during the day but cool at night.
Following are average temperatures for five cities given in Fahrenheit degrees:
San José: High 75.4, Low 61.8 (Central Intermountain Valley)
Alajuela: High 87.4, Low 67.4 (Central Intermountain Valley)
Puntarenas: High .92.5, Low 77.3 (Central Pacific Coast)
Limón: High, 84.3, Low 70.3 (Caribbean Coast)
Liberia: High 96.9, Low 68.5 (North-western Coast & Plains)
There the dry season extends a month or more than it does in the Central Valley.
Along the Pacific Coast of middle and southern Costa Rica (from Tárcoles to the border with Panama) the climate is not entirely dry during the dry season but has frequent afternoon showers. There the pastures stay green throughout the year whereas in most of
Guanacaste all vegetation dries up until the first rains start again.
Practically all of the northern part of the country to the border with Nicaragua is within the big Atlantic Lowland which also encompasses the Province of Limón. There you have rain throughout the year with a short dry period in September and October. The inhabitants of Limon take advantage of this somewhat dry spell to celebrate their Columbus Day Carnival. Where it rains daily, most chores are done in the morning as the showers generally start coming after mid-day. There you won't find the very low humidity that you have in southern California or Central Chile.
From the above you can see that Costa Rica has many climates to choose from and all within easy reach. Thus, if you have a heart or lung problem which can be alleviated by simply changing climate, you can make the change easily and most probably at no great cost. One can say, therefore, that you can literally take your pick of cool, warm, wet or dry weather. It's like having it custom-made to your liking.