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NOUS41 KBOX 191850

Public Information Statement
National Weather Service Taunton MA
250 PM EDT Wed Jul 19 2017

...Hurricane Preparedness Week in Southern New England...
...Rules of Thumb for Southern New England Hurricanes - Part 3...

The National Weather Service has declared this week as hurricane
preparedness week in southern New England. The following is the
third in a series of five statements, the first three with rules
Of thumb for New England hurricanes and the last two with
preparedness actions.

Yesterday we discussed that you should know in a general sense
which side of the tropical cyclone you might be. Typically
heavy rainfall occurs to the left of the storm track, with
strong winds and maximized storm surge to the right of the storm
track. This is not to say to focus on the exact track. The
purpose is get an idea of which hazards you are most likely to
experience at your location.

Here is another rule of thumb for New England hurricanes, and
it works pretty well. If you want to figure out what the maximum
wind gust potential will be at your location you can take the
maximum sustained winds and then add the forward motion of the
storm if you are to the right of the track, or subtract the
forward motion if you are to the left of the track.

In the northern hemisphere, winds circulate counterclockwise
around low pressure areas, such as hurricanes. Thus, to the
east of the center, winds are blowing from south to north and to
the west of the center, winds are blowing from north to south.
Hurricanes that impact New England are usually accelerating
northward along the coast. So, to the east of the center, the
northward motion of the whole storm is in the same direction as
the winds blowing through the storm, which has an additive
effect. To the west of the center, the northward motion of the
storm is opposing the north to south winds blowing around the
storm, which has the effect of reducing the wind gusts observed
at the ground.

Let us look at a couple of examples to illustrate this rule of
thumb, starting with Hurricane Bob from August of 1991. The
center of Bob tracked from Newport Rhode Island northeast across
interior southeastern Massachusetts. Maximum sustained winds at
the time of landfall were 95 mph and it was moving northeast at
25 mph. To the east of the center, one would expect 95 plus
25, or 120 mph gusts. Measured peak wind gusts were 125 mph at
Brewster and north Truro on Cape Cod. To the west of the
track, one would expect 95 minus 25, or 70 mph gusts.
Observations of 65 to 75 mph gusts were common across much of
the northwest half of Rhode Island.

As with any rule of thumb there can be exceptions. There was one
isolated anomaly during Bob. That was within a band of convection
that occurred in Connecticut, which produced an isolated
powerful wind gust of 125 mph in Wethersfield Connecticut.

On September 21 1938, the great New England Hurricane of 1938
Tracked from Long Island to New Haven Connecticut, then straight
north through western Massachusetts. Maximum sustained winds were
125 mph and it was racing northward at 60 mph. Much of southern
New England was to the right of its track. Using this rule of
thumb, one would expect 125 plus 60, or 185 mph maximum wind
gusts east of the track. The Blue Hill Observatory, located in
Milton Massachusetts at an elevation of 660 feet, recorded its
record wind gust of 186 mph.

Tomorrow and Friday, we will concentrate on preparedness actions
for New England hurricanes.


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