Download Quadrant 1 Sea Breeze

Quadrant 1 Sea Breeze: Routing Considerations
Table of Contents
Introduction
Quadrant 1 Sea Breeze Description
2
3
Introduction
Four Sea Breeze Quadrants (Figure 1)
When considering a sea breeze and its probability of successfully developing, think of a typical coastline arranged as above with
Quadrant 1 in the upper left hand corner and the wind from the northwest. A Quadrant 1 sea breeze is generally the strongest of the sea
breezes, and therefore can have the greatest effects on the gradient wind.
NOTE: The example can be rotated in any direction to adapt to your own situation. As an example in Chicago, where the coastline
runs north and south with the land to the west, rotating the quadrants 90 degrees counterclockwise would mean the Quadrant 1
example would rotate and the wind would be from the southwest in Chicago. Also, the examples provided are based on the Northern
Hemisphere, but are equally valid in the Southern Hemisphere. For the Southern Hemisphere, change “left” to “right” and “right”
to “left.”
The following description breaks down the formation of the sea breeze into its developmental stages.
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Quadrant 1 Sea Breeze Description
1. Pre- Sea Breeze Stage
What the wind is doing
The gradient wind is predominant.
Generally, the wind is light to
moderate before the sea breeze fills
in.
How this affects your routing decisions.
Figure 2
Friction from the land slows the
surface wind and shifts it to the left
in the Northern Hemisphere.
Having a left shift closer to the beach may
or may not suit your purposes. That will
depend on which way you’re going and
what you’re trying to accomplish. If you’re
making landfall, it may mean that you’re
better able to lay the mark as you get lifted
on a port tack.
Figure 3
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What the wind is doing
When the surface wind approaches
the water, it turns right due to the
lower significance of friction over
the water; i.e., unaffected by the
forces of friction over land, it
becomes the direction of the true
gradient wind.
How this affects your routing decisions.
Figure 4
As the wind goes further offshore, the
reduced friction over water will allow the
wind to shift right compared to the wind
over the land. Therefore, wind along the
beach will be somewhat more left than
breeze further offshore. Do you want to be
inshore or offshore? Here are some
considerations:
• Will your wind angles be better? Lift
you on a beat? Head you on a run?
Or will the angles be worse, heading
you on a beat or lifting you on a run
or broad reach? Understanding that
it will most likely be more left closer
to shore can help you decide
whether to spend more time offshore
or inshore.
• What is the tide doing? There will
generally be less tide in shallower
water. Depending on your course,
that could be either an advantage or
a disadvantage.
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2. Morning - Sea Breeze begins to develop
What the wind is doing
How this affects your routing
decisions.
Wind speeds within 1 – 2 miles from
shore will probably be reduced due to
the divergence of the wind as it goes
over the water as well as the fact that
you would be in the lee of the land,
possibly sheltered from some of the
wind.
When the WNW meets the NW
wind, it causes a natural
divergence within 1-2 miles of
the shoreline. This area of
divergence creates an area of low
pressure near the shoreline.
Even if the NW gradient wind is
blowing offshore at 10-12 kts,
lighter winds develop along the
shoreline.
Figure 5
At this point you need to have made
your decision: Do you want to be on
the landward side of the area of
divergence, playing the sea breeze? Or
do you want to be on the seaward side
of the area of divergence, playing the
gradient wind?
As the sun heats the land, air
rises over the land and sinks in
this area of divergence (low
pressure).
Figure 6
In order to determine where the outer
edge of the sea breeze is, look for the
calm patch – the area where the air is
subsiding. This is the offshore area of
divergence. Seaward of that calm area,
the winds should favor the gradient
wind direction. Landward of that area,
the sea breeze should prevail
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What the wind is doing
The gradient wind enhances the
offshore flow of the sea breeze
circulation aloft. As the wind
aloft increases, the surface part of
the circulation also increases.
Figure 7
How this affects your routing
decisions.
The sea breeze is building in velocity
and is expanding its coverage seaward.
Keep in mind, however, that the sea
breeze is a self-defeating system. As
the cool air from the sea comes in over
the land, it tends to cool that land along
the coast. The way to keep track of
whether or not the land is warm enough
to support a sea breeze is to watch the
clouds along the beach. If they are
growing, the sea breeze is building. If
the clouds are diminishing, the sea
breeze is faltering.
Expect a shift from offshore winds
(gradient winds), followed by a short
time of lull, and then a gentle sea
breeze to fill in perpendicular to the
land.
Before the first puffs of sea
breeze are felt, the surface winds
will be very light. The first puffs
of the sea breeze are generally
perpendicular to the coast.
Figure 8
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What the wind is doing
How this affects your routing
decisions.
As the morning progresses, expect a
stronger sea breeze if the weather
inland remains warm, and expect the
offshore outer edge to move seaward.
If the air continues to be unstable,
the sea breeze circulation will
grow larger and the sea breeze
will become stronger, expanding
further offshore.
Figure 9
There will always be an area of
wind holes between the inshore
sea breeze and offshore gradient
wind during a Quadrant 1 sea
breeze. Do not get stuck inbetween and in the wind holes.
NOTE: This may not be a constant
increase. Quadrant 1 sea breeze
circulation can go through a cycle of
strengthening and weakening as it
builds. Watch the clouds to determine
how it is developing.
Your strategy may take you seaward of
this edge to find gradient wind, or
shoreward of this edge to find the sea
breeze. The problem is when you’re at
the edge.
Figure 10
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What the wind is doing
How this affects your routing
decisions.
As the speed of the sea breeze
increases and thus the forces of
friction over both land and sea
become more significant, the sea
breeze over the water can rotate
right, perhaps going as far right
as to create a SW wind (in this
example).
Figure 11
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3. Afternoon - Sea Breeze begins to fade
What the wind is doing
If the ocean is cool, a surge of sea
breeze will cool and stabilize the
land, choking off the circulation.
This is the self-defeating nature of
sea breezes: the cooling air from the
water slows the sun’s warming
process of the air over land.
The sea breeze weakens, and then
waits for another surge of rising air,
which can be accompanied by a
significant left oscillation, then
builds again, etc. In order to get the
right-hand / left-hand shifts, the sea
breeze would need to be relatively
charged up. If it’s a weak system, the
wind may not shift around.
How this affects your routing decisions.
Expect the sea breeze to decrease in speed.
If you have been playing the sea breeze, you
will want to work your way offshore at
some point so that you are not trapped
inside during the final dying stages of the
sea breeze.
Figure 12
Make sure that you’re offshore prior to the
sea breeze ending for the day. Getting back
into the gradient can help you keep way on
while others inshore are struggling with the
dying sea breeze.
Figure 13
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What the wind is doing
Eventually, as the sun begins to set
the sea breeze will completely die.
How this affects your routing decisions.
The gradient will eventually return, but the
boats on the shore will be the last to get it.
Notice that the cumulus clouds have
disappeared over land.
Figure 14
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©2010 L. Roberts and B. Biewenga
(203) 389-4440
Last Modified: April 14, 2010