Tight Pressure Gradient Producing Gales & Coastal Flooding

The pressure gradient along the northeast corridor remains very tight and will continue to remain tight probably through the weekend. Even though the hurricane will have no direct impact it will indirectly continue to add wind and rough ocean seas offshore which only puts more pressure on higher than normal tides and beach erosion. nam18

By pressure gradient we mean basically lots of isobars. When you have a large change in pressure over a relatively short distance, you create wind. The tighter the gradient or the bigger the change in pressure over shorter and shorter distances means winds get stronger and stronger. In Hurricane Joaquin the pressure in the northwest Bahamas is 1000 mb while the pressure in the central Bahamas is 935 mb or a 65 mb pressure change in less than 200 miles..that is huge. That’s why you get 130 mph winds. Here of course it isnt extreme but we have a 1040 mb high in Eastern Canada and pressures around 1008 mb over North Carolina. That’s a 32 mb change over 600 miles or so and this is enough for 20 to 35 kts with gusts to 45 kts or gales from Southern New England down to North Carolina. The fetch of northeast to east winds is long from out over the Atlantic. Today is the second full day of such a fetch and it will take us through Sunday making it 4. That is very unusual to have such a prolonged period of northeast gales but there you have it. The hurricane will push into that gradient over the weekend which will increase winds out over the coastal waters and cause tidal flooding problems to continue through at least Sunday.

With regards to rain there will be some today into Saturday morning but beginning Saturday afternoon dry air should begin to work southward forcing the rain to dry up as the action shifts south and east. Sunday could very well turn out to be no worst than partly sunny and breezy with highs in the 60s. Until the it is rain, windy along the coast, and raw with temperatures not out of the 50s.

namprecip

The nam at least spreads out about an inch to an inch and a half of rain with more to the south and less to the north over 36 hours which is great as the rain will really get a chance to soak into the ground.

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