Puerto Rico meets the Saharan Desert

IWhen you think of Puerto Rico, you probably think of tropical beaches, bright blue water, and warm humid weather.  So what could the Sahara Desert possibly have to do with a Caribbean island?

Believe it or not, Saharan dust can travel west across the Atlantic to as far as the Gulf of Mexico.  It's called the Saharan Air Layer (SAL), and it affects the daily lives of people in the Caribbean and Central America.

It just so happens that two of my former roommates (and current best friends) are from Puerto Rico. My friend Janice let me pick her brain on the topic, and her first reaction when I asked what it was like when the SAL blew in was, "Oh no! You can't go outside on those days!"

She says the dust is a killer for people with allergies and asthma.  With the dust comes pollen, microorganisms, bacteria and even insects.  She says it also means, "Don't wash your car!  With all the dust, cars and everything outside can be covered."

It sounds like living through a low-level dust-storm... in the middle of the tropics!  Most daily activities continue as normal, but visibility can be low.  So much for that clear view of the beach.

It's something most visitors and tourists have never heard of, yet it's a regular occurrence.  There are a plenty of published papers and web articles on the SAL, but Janice also happens to be a meteorologist for the National Weather Service... so I asked her for a basic explanation.

You've probably heard of the trade winds?  Well, in northern Africa, air movement is predominantly from east to west.  In other words, winds blow over the Saharan Desert and into/across the Atlantic.  The dust is light and easily carried by the winds across the ocean.  You can even see the SAL on satellite.

It's strongest from May to September and can cover 2000-5000 km.  It comes in waves (NOAA says every 3-5 days), but Janice tells me the worst month in Puerto Rico tends to be July.

Although the dusty days keep some Puerto Ricans inside, there are a few pros.  Janice says it helps fertilize the soil and provides nutrients for phytoplankton in the ocean.  But maybe the biggest pro?  She says, "Sometimes this phenomenon can be beneficial for the island, because it helps weaken tropical systems that are a threat to Puerto Rico."  Hurricanes and tropical depressions don't like dry air, so the dust sometimes weakens them before they make landfall.

Monsoon Season in India

Diptendu Dutta - Getty Images

You've probably seen massive flooding in India covered on the news at some point in the past few years. It seems so far away (for many of us) that it's hard to imagine recurring devastation in a major city like New York or LA. But for a lot of India, it's expected  - and in some cases even welcomed - on an annual basis. 

As a meteorologist with a love for travel, I've always wondered how flooding became such a normal part of Indian culture. You see video clips of people walking, biking and driving through knee deep water to get to work. It's the complete opposite of the motto from the National Weather Service, "turn around, don't drown."

So what causes such heavy rainfall there almost every year? It's called the monsoon season. Despite what most people think, a monsoon isn't a heavy rainstorm. The term monsoon actually refers to a seasonal shift in wind direction. 

In India, winter winds come from the north, bringing in cooler and drier air from the mountains. In the summer, the winds shift and come from the south, across the Indian Ocean. Similar to the way we pick up moisture from the Gulf of Mexico, it's warm and humid. When that air hits the Himalayas, it rises, cools, and dumps out all its moisture as rain.

According to NOAA, the monsoon season in India lasts from June to September. Western and central India receive about 90% of their annual rainfall during those months. Northwestern and southern India get 50-75%. In terms of totals, we're talking about an average of more than 11 inches of rain per month... and some locations see over 100 inches of rain per season!!

With such heavy rainfall, you'd think summer would be a less-than-ideal time to travel to India. On the contrary, Travel & Leisure has published an article on some of the best places to go to enjoy the green and lush environment despite the flooding.

Top of their list is the country's capital, Delhi.  They say the rain cleans the city's notoriously dirty air, and "there's nothing like seeing Lodi Gardens, the Mehrauli Archaeological Park, and the gorgeous grounds of Humayan's Tombs freshly washed by the monsoon."  Also on the list is Goa, Shillong, Spiti, and Mandu.  Mandu sounds particularly intriguing to me.  The article says, "After a day biking through the rain among solitary, mossy ruins, and climbing crooked staircases to empty ramparts overlooking monsoon-filled lakes... it's the India you didn't know you'd been dreaming of."

For people who live in India, it might be a dream come true for a different reason.  This year, the monsoon season is bringing a much needed-end to a drought.  ABC Australia reports that drinking water was becoming scarce.  The India Meteorological Department says much of the country has been in a severe water crisis, and after two years of waiting, this monsoon season should bring above average rainfall.

Diptendu Dutta - Getty Images

That's good news for farmers.  In the cities, however, needed rainfall can quickly turn to massive flooding, due in large part to the poor drainage systems.  When the water gets too deep, you can imagine the reaction.  Cars are left abandoned in the streets, workplaces close, and India is once again a world-wide news headline.  Just last week, the Weather Channel reported 7 dead and over a million displaced after flooding in the state of Assam.  It's a fine balance that can be easily tipped when it comes to Mother Nature.