Another weak front


Boxing day FROPA
A plot of data measured with my PWS from midnight Christmas morning to midnight on the morning of the 27th. This captures the passage of a cold front at around 3am on boxing day.

 Ahead of the previous front in the early morning hours on Boxing day, Christmas eve and Christmas were unseasonably warm. High temperatures reached the mid-70s when they are typically in the 68-71°F range. This is because of a warm, humid southerly and southwesterly flow ahead of the cold front in what is known as the ‘warm sector’. In fact, this warm/humid flow was slowly increasing temperatures through the night before the cold front passed – temperatures increased from 71°F to near 73°F around midnight, ahead of the front.

The cold front then passed around 3am. Winds shifted from the south/southwest to the northwest and while there was only a modest decrease in temperatures (from 72°F to 68°F), the dew point dropped off significantly (from near 70°F to near 55°F) indicating much less humid air blowing in behind the front. The lower humidity and slightly lower temperatures, in addition to the breezy northwesterly winds made for a Boxing day that felt much cooler than Christmas eve or Christmas day, despite temperatures only decreasing slightly to near seasonal levels.

12z ECMWF 20141230 new years eve front
12z December 30th ECMWF model depiction of cold front near Bermuda at 5am December 31st local time. Cold front indicated by the blue flagged line. White streamlines and shaded isotachs (kts). Image generated in Wundermaps.

Another cold front is expected to pass early in the morning on New Year’s eve. Showers and moderate to strong southwesterly winds ahead of the front are already affecting the island. They allowed high temperatures to recover into the mid-70s again and the dew point has begun to increase on the 30th/today. As the cold front passes early in the morning on New Year’s eve, winds shift from southwest to northwest then north gradually decreasing from strong to moderate by evening. Unlike the Boxing day front, where there were several showers ahead of and along the front, it is possible that the New Year’s eve front will be associated with patchy rain or showers following the front in addition to those along/ahead of it. Any wet weather is expected to clear by early evening – in time to salvage New Year’s festivities.

A small craft warning is in effect through Wednesday morning for strong winds of 20-25kts, and seas near 9ft outside the reef. For the latest official weather information see the Bermuda Weather Service.

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