Extreme Weather Event Yeti is about to come to a climax over eastern North America with snow exiting the Atlantic coast today followed by a continuation of the extreme cold. Readings in the heart of the cold blast broke daily records this morning and in some places could break all-time March records tonight.
Yeti has been rampaging back and forth across the eastern two-thirds of the US for the past month. He is the personification of the polar vortex, a swirl in the middle of the atmosphere that normally resides in northern Canada, but this winter has pushed south into the eastern US.
A hundred inches of snow in Boston, traffic-snarling freezing rain in Dallas, and numbing cold everywhere in-between have been Yeti’s calling cards.
There’ll Be A Change In The Weather
The weather pattern over the United Sates is changing due to El Niño Eggplant in the middle of the Pacific Ocean. A low latitude jet stream will start bringing rain to California next week, and that will usher in a new regime featuring a retreat of the polar vortex to northern latitudes.
By Sunday, the heavy snow will be over and the cold beginning to abate. By the end of next week, temperatures will be near or above normal in most of the country.
The Northeast Corner Of The Caribbean: Hurricane Alley In The Summer, But Beautiful In March
Snow, wind, and cold get the headlines, but many locations are experiencing fine weather. Decoded Science will feature one such place every Friday, along with updates on the nasty stuff.
The Leeward Islands, so named by the British during their period of dominance in the region, are the northeasternmost of the semi-circle of islands that surround the eastern half of the Caribbean Sea.
A more proper designation for these specks of land is the Lesser Antilles. Larger islands to the west (Cuba, Puerto Rico, and Hispaniola) comprise the Greater Antilles.
The name derives from the depiction on 16th century sailing charts of a presumed large land mass called Antilia. The Entire archipelago of the Lesser Antilles stretches south and then west to the north of Venezuela.
In the summer, the northernmost of these islands are in the path of many hurricanes. But in the winter, the weather couldn’t be nicer.
All the islands are tiny, with coasts that face both the Atlantic and the Caribbean. Normally, surf’s up on the east-facing beaches, while the west-facing ones are smooth as glass.
The North Atlantic Gyre
A huge anticyclonic vortex (there’s that word again) covers the North Atlantic Ocean. To the north, the jet stream and associated westerly winds at the surface waft and sometimes howl from North America to Europe. To the south, the ‘trade winds,’ easterly winds that were used by traders in sailing vessels before the development of automated locomotion, blow from Africa to the New World.
To complete the circulation, southerly winds near the US coast and northerly winds off northern Africa bring cold water currents on the eastern side and warm water currents (the Gulf Stream) on the west side of the ocean.
Winter Weather In The Northern Lesser Antilles
In the zone of the trade winds, the islands of the northeast Caribbean have generally fair weather in the winter. The humid oceanic flow brings showers at any season, mostly light in the winter and heavy in the summer. The temperature settles in to about 80 degrees, just about the same as the ocean water.
In the summer, their location puts these islands in the paths of many hurricanes which follow the trade wind portion of the North Atlantic gyre.
Dead Center Of The Northern Lesser Antilles: Antigua
If you plopped yourself down smack dab in the middle of the Leeward Islands, you would land on Antigua, at 17.5 degrees latitude.
It’s a tropical paradise with good swimming conditions all year. In fact, there are 365 beaches on Antigua, so if you move there you can go to a different one every day of the year.
Hurricanes In Antigua
Summer brings little change in temperature on Antigua, but big changes in rainfall and wind. Rainfall increases from less than two inches per month in March to over 11 inches in September.
On average, Antigua gets hit by a hurricane every six and a half years, and the average wind speed in these hurricanes is 105 miles per hour.
The Date To Stay Away From Antigua
August 21 is a notorious date in Antigua: Four hurricanes have struck the island on that date, two of them powerful category three storms.
But in mid-March, there’s nothing to worry about ….. except possibly earthquakes.
The following was contributed by geoscientist Jennifer Young.
Tectonic Activity In The Lesser Antilles
If you want to understand what’s going on in the Lesser Antilles (or whatever you choose to call them) you could do far worse than look at the Smithsonian Institution’s fabulous interactive map of Our Dynamic Planet. A screenshot from the map is below – on it you can see the elegant curve of the island arc which marks the eastern boundary of the Caribbean plate.
The yellow line marks a subduction zone, one of just two (or possibly three but that’s a topic for another day) in the Atlantic Ocean. Here, the cold, dense oceanic crust of the Atlantic descends beneath the Caribbean plate. The fact that the Earth is round accounts for the graceful curve of the island chain which is the Lesser Antilles and its many island groups.
Trouble In Paradise
The gorgeous, rugged scenery of the Caribbean islands comes with a warning. See those red triangles on the map? They’re volcanoes which have erupted in the past century or so. The red triangles with the black dots? They’ve erupted in the last two millennia. And the white ones? They’ve erupted in the past 10,000 years.
The volcanoes are the result of the subduction process. The descent of the subducting plate takes rock to depths where the temperatures and pressures are such that it melts. Molten rock, being more buoyant than that which surrounds it, rises to the surface — and breaks out in the shape of volcanoes. The Smithsonian’s Global Volcanism Program lists 17 of them in the island arc.
The evidence suggests that these volcanoes don’t erupt that often (the GVP notes just 18 eruptions in historical time) but when they do it’s time to sit up and take notice. They’re big beasts, and potentially deadly. In 1902, two of them erupted: Mont Pelée, on Martinique, killed over 29,000 people and La Soufrière, on St Vincent, chipped in with a death toll of over 1,600.
Nothing’s erupting just now, though you might want to take a look at the black circles on the map. They’re earthquakes. But again, rest assured: there’s no evidence that this subduction zone can generate the really large earthquakes which occur elsewhere and the largest on record is M7.5. It wouldn’t be true to say that there’s no risk from Mother Nature in the Lesser Antilles; but it certainly isn’t as large as it is elsewhere.
Fair And Foul Weather For The Rest Of March
As the season turns, there will be more fair weather and less foul in the northern hemisphere. As the jet stream flattens and relaxes next week, the next extreme bad weather event is more likely to involve lightning, hail, and the threat of tornadoes than snow and cold.