Where are the Christmas Winds?

The climate of Trinidad is strongly influenced by the North Atlantic High, also referred to as the Bermuda High or Azores High, based on its seasonal positioning. During the fall season, the Atlantic High moves southward in response to the southward push of low pressure systems and their associated cold fronts over North America and the North Atlantic. The high’s southward position and lower sea surface temperatures, north of 10°N, result in strong easterly trade winds across the eastern Caribbean during winter. This increase in winds typically occurs around mid to late December, giving them the seasonal name: the Christmas Winds.    Subtropical Ridge Index Western Atlantic NCEP

Over the past week, heights over the western Atlantic have increased. A 200mb (200hPa) height means the height at which the pressure is 200mb. An increase in heights aloft will correspond to high pressure at the surface and rising temperatures.

Both the ECMWF and GFS forecast models indicate continued above normal heights/pressures over the southeastern U.S and far western Atlantic through Christmas, due to a persistent 500mb ridge. The position of that ridge (NW of the eastern Caribbean) and the stalled surface boundary offshore the southeastern U.S. should moderate trade winds offshore Trinidad through the Christmas holiday. Next week, there is potential for a surge in the trades across that region as surface high pressure moves east into a more favorable position, north and north-northeast of the eastern Caribbean. This positioning is more favorable since the trade winds blow from subtropical high pressure systems (with clockwise circulations) to lower pressures along the equator.

Here is a brief look at the long-range forecast..U.S. 8-10 day 500mb mean height anomalies for ECMWF (left) & GFS (right) forecast models valid for the time frames indicated below:

U.S. 8-10 day 500mb mean height anomalies
Thursday Dec. 29th, 2016 – Saturday Dec. 31st, 2016
penn500mbmean_12-30-16
Friday Dec. 30th, 2016 – Sunday Jan. 1st, 2017