Local Conditions

By Bob McCann, 1964 & 1965 Sears Cup Winning Crew


During the month of august, the Marblehead area is usually under the influence of a light
(5-10 knots) southeasterly sea breeze. In the late afternoon, this breeze will follow the sun
to the south, eventually coming from 180º to 210º. The thermal heating of the land during
the morning and early afternoon creates the sa breeze. Often in the early morning, there is
little or no wind. Until the sun has had time to heat up the land, the thermal effect and
resulting sea breeze do not come into play.

It is often said that Marblehead is subject to a prevailing southwest breeze. However, in
the early morning, prior to the thermal effect taking place off Marblehead, the city of
Boston (southwest of Marblehead) heats up enough to block the prevailing southwest
breeze. Any southwesterly is typically diminished by 9:00 a.m. The only exception is
when the southwesterly breeze is strong and the sun is blocked by enough haze to allow
the southwest breeze to continue through the day. This is an unusual situation and only
occurs approximately three or four days in August.

Should the conditions allow the prevailing southwesterly to continue throughout the day,
you might expect it to back towards the east, slightly, as the land heats during the day. A
backing from approximately 210º to 180º is not unusual. As the land cools off later in the
day, the southwesterly will again come in from approximately 210º.

Assuming that the southwesterly breeze is not able to reach the Marblehead shore,
typically between 11:00 a.m. and 1:30 p.m., the sea breeze will be generated by the
thermal effect. The general direction of the sea breeze is 165º. Approximately half the
time, the sea breeze will back during the early afternoon, to approximately 150º – 160º.
As the afternoon goes on and the city of Boston cools down, the breeze will begin to
clock to the right, eventually settling, in the late afternoon, in a general southerlysouthwesterly
direction (showing the effect of the prevailing southwesterly breeze).

There are two other wind conditions which, though not generally prevalent in August,
should be mentioned. In the event that a cold front comes through, resulting in dryer,
cooler air, you may expect to see a north-northwesterly breeze. This breeze typically lasts
for 2-3 days. On the first day following the cold front, the northwesterly breeze can be
quite strong (up to 20 knots). The breeze will oscillate between 285º and 335º. The
oscillations are generally 4-6 minutes apart in time, and depending on the location of the
cold front and velocity of the breeze, may be predicted. In order to predict the timing and
direction of the oscillations, you should spend some time prior to the start taking
numerous wind directions and checking the timing between each and every change of
direction. With enough attention, you will be able to predict the wind shifts to your
advantage. In addition, while you are checking the wind shifts prior to the start, you
should observe the water coming off the land. By watching closely, you will be able to
pick up the velocity and directional changes on the water..

Depending on the strength of the cold front, the northwest breeze will last either 2 or 3
days. On the second or third day, the northwesterly will typically continue until early
afternoon at which time the heating up of the land will cause it to die and the sea breeze
to fill in. During the transition, it is not uncommon to sea the northwest breeze blowing
off-shore with the sea breeze blowing onshore, resulting in approximately 100 yards of
flat calm between the two breezes. The sea breeze will typically take over as the day goes

Occasionally (though extremely rare in the month of August) a storm system will pass
offshore resulting in a northeasterly breeze with 2 or 3 days of rain. In this situation, you
may expect that the winds will blow out of the northeast at approximately 20-30 knots. If
such a storm should come in during the series, you may expect fairly high seas with very
steady winds.


The Marblehead area is subject to extremely tricky current patterns. In general, close
inshore, the currents run directly in and out of Salem Harbor (past Cat Island towards
Halfway Rock). This flow is in general northerly (flood)/southerly (ebb) direction.
Further offshore, the currents are more generally affected by the direction of the flow
between Boston Harbor and Gloucester. These currents, near Halfway Rock and further
out, flow in a general westerly (flood)/easterly (ebb) direction.

In between these two currents are numerous areas where the tides are somewhat
unpredictable. Your best bet is to note the direction and strength of the current on the
lobster pots where you are sailing. The currents inshore, near Satan’s Rock and the
Gooseberries, are generally lighter than the currents in the Open Bay area, which may run
as strong as 2.5 to 3.5 knots. The strong currents are generated by a rise and fall in the
tide of approximately 9 feet.