Skirting the Pacific High

Whether undertaken while racing or
cruising, the downwind passage from the western coast of North America
to Hawaii is one of sailing's classic bluewater voyages. Arriving among the lush, green, volcanic hillsides of the island chain is as good as it gets.

For several solid reasons, most Hawaii races begin in July.
Temperatures are mild, the days are long, and the jet stream has moved
north, as have the tracks of the low-pressure systems that follow it.
These factors all influence the development of the summer's pre-eminent
atmospheric feature, the Pacific High. This high-pressure system
usually establishes itself over the North Pacific by late June.
Plotting the quickest and most efficient route around its windless
center--a veritable parking lot--is the key to a successful trip.

Unfortunately, this lot is usually stationed directly across the
shortest route to Hawaii from many popular U.S. West Coast departure
points and starting lines. Furthermore, the high isn't static but can
change shape, size, and position several times during the course of a
passage.

The Pacific's traditional, steady, 18- to 25-knot northeasterly trade
winds spin off the lower section of this circular weather system.
However, the first hurdle in any passage from North America to Hawaii
is taking leave of terra firma and its effects on the local breeze and
latching onto the "gradient" wind generated by the Pacific High.

The first major decision is where and when to cut the corner at the
bottom of the high to "cross the ridge" into the dependable trades.
This is a tricky call: You don't want to sail too close to the high on
the shortest route and risk losing the breeze, but you also don't want
to add any unnecessary distance by sailing too far south in search of
steady wind pressure.

In practice, boats hold course on starboard jibe while navigators study
the spacing of the isobars to determine the route to follow for the
optimal wind strength, in effect choosing a lane for the islands. This
choice has to be made early, sometimes even before reaching the
gradient wind of the high. Once the initial waypoint is set, you're
committed to your lane. Navigators spend the next few days and nights
looking for any sign of instability or movement of the high that might
alter their plans. Clues can be found by monitoring the upper-air,
500-millibar charts, which provide a graphic preview of wind patterns
to come.

If you sail too close to the center of the high, winds begin to soften,
and you must sail higher and tighter angles to maintain good boat
speed. Especially when racing, jibing onto port is a poor option
because you can end up pointing well behind the boats that crossed the
ridge farther south. It can almost appear that you're returning to the
mainland. That said, because the breeze will continue to falter, the
longer you wait to bail out of a bad situation, the worse it gets.
Meanwhile, choosing the correct lane means nice, steady pressure along
the shortest possible course.

Once the ridge has been crossed and the trades fill in on a steady
bearing of about 070 degrees, the toughest part of the navigator's job
is over. Most crews will then maintain a starboard jibe until reaching
a position dead upwind of Hawaii. From there, it's wise to sail the
favored jibe, which is determined by where the pressure or wind
strength is expected to be strongest.

In last summer's Pacific Cup race, the high-pressure system was
particularly round and stationed in a more northerly position than
usual. With a staggered start over the week of June 28 to July 2, the
first boats set a more traditional southerly course out of San
Francisco. When the four-boat racing class that included Icon
started on July 2, the high had slid north, and boats were able to sail
the shortest route and maintain breeze. Some even sailed north of the
shortest route on a heading that in other years would pass through the
windless center. Meanwhile, the isobar spacing along the southern route
was wider, resulting in lighter winds of insufficient strength to
overcome the distance sailed. Nonetheless, the 16-knot average wind
strength we saw on Icon for much of the trip made for some great
downwind sailing.

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Physician Kevin McMeel is a seasoned offshore sailor. He assisted
British sailor Ellen MacArthur with navigation aboard the 110-foot
catamaran Kingfisher 2 in her 2002 Jules Verne round-the-world attempt, a voyage that ended after a dismasting off Australia.