'tis the season

 

 Ah, Hurricane Season! Hurricane Matthew, the fifth hurricane of the season, was briefly a Cat 5 early this morning. Since then, Matthew has slipped back to a Cat 4 and may weaken even further before it hits Jamaica.

When then-Tropical Storm Matthew went by well south of us, it brought us winds up to about 35 mph, rain and one of the most beautifully intense thunderstorms I've ever seen. If the storm hadn't frightened the dogs so much, I would have loved it.

Even as we send positive energy into the universe for people in Jamaica, eastern Cuba and Haiti, we are also grateful for what Matthew was - small - and was not - big and dangerous - when it went by us.

We are actually very fortunate here in Puerto Rico and especially here on the west coast when it comes to hurricanes. Most of the time the storms that form off the Horn of Africa are either tropical depressions (winds less than 39 mph) or tropical storms (winds 39-73 mph). Puerto Rico is usually the wedge that divides storms going north along the east coast of the US or south into the warmer waters of the Caribbean and Gulf of Mexico.

One reason these storms don't usually develop in to hurricanes until after they pass us is slightly cooler ocean temperatures between Africa and Puerto Rico. For one thing, the Atlantic is deeper and colder that the Caribbean. But there is another factor as well: Sahara dust.

Dust from the Sahara Desert streams across the Atlantic in the upper atmosphere. At times this dust cloud is heavy enough it can be seen from space. (A friend of ours used to work at the observatory in Arecibo. Part of his job was to monitor the Sahara dust.) This dust cloud actually shades the waters of the Atlantic just north of the equator. This shade keeps the water several degrees cooler than it would be without the cloud. This in turn means the tropical storms crossing the Atlantic have less warm moist air, which they depend on for development, to feed on until they hit the Caribbean. Thus, they frequently remain tropical storms, not hurricanes, when they hit Puerto Rico. (Another aside about the Sahara dust: this stream carries nutrients from the Sahara that help feed the Amazon forest. We are connected in ways we can can't even imagine!)

On those rare occasions the tropical storms do become hurricanes before they hit Puerto Rico, they are usually small and not well developed. Because they travel from east to west. they expend a lot of their energy - and rain - crossing the island. That means the eastern third of the island gets hit much harder than we in west do. A few years ago when Hurricane Irene passed over, the east side of the island had 60 mph winds and nearly 13 inches of rain. By the time Irene got to us there was no rain and 40 mph winds. That's what I meant by being fortunate here in the west.

And one more digression if I may: we had 40 mph, even 60 mph winds, when we lived in Michigan., usually when it was somewhere between 0 and 10 degrees. Here we 40-50 mph winds - and it's still 80! It's much easier to tie stuff down when you're not wearing thick gloves or your fingers aren't numb or sticking to whatever it is you are trying to tie down.

Here's hoping everyone in the path of Matthew hunkers down and is safe.