Why is it so rainy in El Yunque – travels in Puerto Rico

This week, the entire engineering team at Yext went on a trip to Puerto Rico. Three nights at a beach resort, all expenses paid for.

What?! As an intern? No way! That was my reaction when I first heard about it. Friends at other software companies boasted about corporate housing, gourmet meals, and pantries stocked full of snacks of every kind, but Yext’s Puerto Rico offsite takes the cake.

The Resort

San Juan, the main city in Puerto Rico, is a 4 hour flight from New York. Puerto Rico is a popular destination because it’s a US territory, so you don’t need to worry about things like visas or international currencies. Also the drinking age is 18, rather than 21 for most of the US.

The resort was located 1 hour from San Juan, in the Fajardo region. I had never been to a Caribbean resort before, but the experience was more or less identical to my preconception of what a resort should be like. Along with my fellow engineers, we had a good time swimming in the beach, playing beach volleyball, and drinking lots of mojitos.

Here’s me on the beach:

Since this is a company offsite, there were some serious activities too. For half the day, senior Yext engineers gave tech talks on things like domain driven design and how to write integration tests.

After the Resort

For me, the amount of fun I have at a resort is not constant. The first day at the resort is the most amazing thing ever. Then on the second and third day, when you redo the same resort activities, the excitement wears off. I think if I spent a week at the resort, I’d be pretty bored by the end of it.

After the 3 days that were officially scheduled, some of the engineers decided to stay at the resort for the weekend. I joined a group that rented a car and drove to El Yunque — a tropical rainforest not too far away. After that, I spent another day exploring the city of San Juan by myself before getting on the plane back to New York.

El Yunque was surprisingly rainy. Even though we knew it was a rainforest, the amount of rain caught all of us off guard.

Standing on a lush green mountainside, you could see the dark clouds releasing a constant downpour of rain. Yet in the distance, the beach resort remained warm and sunny. The skies cleared up the moment we left the rainforest.

It seemed all the rain was concentrated within the boundaries of El Yunque national park, as if artificially constrained by a force field.

So why is it rainy in El Yunque?

The curious climate of El Yunque intrigued me. When I got home, I did some research on why it behaved this way.

A quick Google search gave me this precipitation map, which confirmed my suspicions:

Figure: Mean Annual Precipitation of Puerto Rico in 1963-1996

The purple region in the northeast is El Yunque. It receives 120 inches of rainfall a year, which is 3 times more than San Juan.

It might also be worth looking at a relief map of Puerto Rico:

The rainforest area is on a higher elevation than the surrounding region. So the rain falls where there are mountains. Gotcha.

This phenomenon is called orographic precipitation (orographic means relating to mountains). When warm and humid air is forced up a mountain, it cools and forms clouds, which then precipitates. The other side of the mountain experiences a rain shadow effect as the descending is devoid of moisture.

Also, in the Caribbeans, the trade winds tend to blow from east to west. This explains why El Yunque is a rainforest, but there are higher mountains in other parts of the island which are not rainforests.

Actually, in retrospect this seems like a fact we all learned in grade school. I don’t know what explanation I was expecting, something fancier?

In any case, this mix of geographical and weather conditions gives us a unique and beautiful landscape — and the only tropical rainforest in the US.

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