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Nor'easter: Here's my layman's
try at a Nor'easter definition. A Nor'easter is counter-clock wise turning
cyclone (a storm system circulating around a center) as opposed to a
hurricane which turns right in the northern hemisphere. Nor'easters are
spawned by a very curvy Jet Stream that dips far south allowing cold
arctic air to meet warm air. The warm air rises over the cold, creating
instability up high and an area of low pressure below. Larger temperature
differences create greater turbulence. Once the system is formed, the
earths rotation causes the air to circle around the center (similar to
when you drain the water out of your bath-tub). This creates the northeast
wind, hence it's name nor'easter. They typically form near the Bahamas or
north of Cuba, along the Appalachians or off Cape Hatteras. The Jet Stream
plays a very important role also in the strengthening of the storm. As the
incoming air rises around the center, the Jet Stream whisks it away
further increasing the speed of the incoming air. The faster the air moves
the faster the barometric pressure drops. Weather forecasters call a 24
millibar drop in 24 hours "The Bomb". Normal Jet Stream winter
pattern is to follow the coast and consequently drags the storm northeast
ward. Some time a High further north blocks its path and so it churns over
the ocean for a long time sending beach-eating waves onshore. During the
October to April nor'easter season February is the busiest month.
Researchers say the biggest ones occur in October, January and March. What
nor'easter don't achieve in wind-speed as compared with hurricanes, they
achieve in duration (up to a week) and size (up to 1000 miles or more in
diameter).
WIND SPEED/SEA HEIGHT RELATIONSHIPS
|
| Wind Speed |
Sea Conditions |
| 0-3 KTS |
SEA LIKE MIRROR |
| 4-6 KTS |
RIPPLES, LESS THAN 1 FT |
| 7-10 KTS |
SMOOTH WAVELETS, 1-2 FT |
| 11-16 KTS |
SMALL WAVES, 2-4 FT |
| 17-21 KTS |
MODERATE WAVES, MANY WHITECAPS, 4-8 FT |
| 22-27 KTS |
LARGE WAVES, SPRAY, 8-13 FT |
| 28-33 KTS |
HEAPED SEAS, FOAM FROM BREAKING WAVES,
13-20 FT |
| 34-40 KTS |
HIGH WAVES, FOAM BLOWN IN WELL MARKED
STREAKS, 13-20 FT |
| 41-47 KTS |
SEAS ROLL, SPRAY MAY REDUCE VISIBILITY,
13-20 FT |
| 48-55 KTS |
VERY HIGH WAVES, WHITE SEAS, OVERHANGING
CRESTS 20-30 FT |
| 56-63 KTS |
EXCEPTIONALLY HIGH WAVES, 30-45 FT |
| OVER 63 KTS |
AIR FILLED WITH FOAM, SEA COMPLETELY WHITE,
OVER 45 FT |
THIS CHART IS BASED ON CRITERIA USED BY THE WORLD
METEOROLOGICAL ORGANIZATION. MARINERS SHOULD REALIZE THAT THESE VALUES ARE
REACHED AFTER WINDS HAVE BLOWN STEADILY OVER A LARGE AREA FOR AN EXTENDED PERIOD
OF TIME. ALSO, THE VALUES GIVEN ARE AVERAGE OBSERVED WAVE HEIGHTS, NOT THE
HIGHEST THAT MAY BE SEEN FOR A GIVEN WIND SPEED.

Revised:
January 14, 2004
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