Under Pressure

2015-08-17 16:44:25.000 – Ryan Knapp, Weather Observer/Staff Meteorologist


After what has been a fairly mild summer (at least here in northern New Hampshire), this week the thermostat has been cranked. A large dome of high pressure has built over the Eastern Seaboard where it will sit in the coming days setting up as a Bermuda High. The anticyclonic (ie, clockwise) flow around the high will mean warm, moist air from the Caribbean Sea and Gulf of Mexico will continue to stream northeast keeping things warm and muggy in the coming days. Short-term, this set up of summer-like weather might sound ideal to some people. Long-term though, this set up brings an increasing potential for severe weather and hurricanes.

While the periphery of the high is responsible for hot, humid, and hazy conditions on the East Coast, towards the center of the high in the Atlantic, air is sinking causing it to dry and warm. This sinking motion suppresses cloud formation over the ocean, allowing sunlight to warm the waters in the Atlantic. The longer the high is able to stick around, the more it is able to allow sea surface temperatures to rise around the inter-tropical convergence zone (or ITCZ for short), which in short, is the breeding grounds for the formation of tropical storms and hurricanes. As an area of low pressure forms or moves off the horn of Africa and encounters these warm waters, it intensifies. It then is steered clockwise around the large dome of high pressure towards the Caribbean and Eastern US. As of this writing, there is already a disturbance forming which will need to be monitored in the coming days for its potential to develop into a possible hurricane later in the week.

While hurricane potential is something to eye on in the really long-term, short-term, the hot and humid conditions will be a primer for severe weather in the coming days. As a cold front slowly approaches from the west, the atmosphere will become increasingly unstable, heightening the risk of daily showers and thunderstorms for the region. Convective activity will be spotty on Tuesday but as the front approaches for an expected passage on Friday and Saturday, activity will become more and more widespread. As the warm weather increases outdoor activities, those playing outdoors should take precaution and keep an eye on the forecast as well as the sky in the coming days.


Ryan Knapp, Weather Observer/Staff Meteorologist

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