FPB Series

A New Paradigm for Cruising

Design Objectives

FPB 64

FPB 83

FPB 83 On Deck

FPB 83 Interior

FPB 83 Systems

Passages

How Things Are Working Out

Hawaii Back to the Mainland

Weather Logic

The trip from Hawaii to the mainland revolves around the status of the Eastern Pacific high pressure system. When you're headed towards Hawaii, the high pressure produces trade winds from the easterly quadrant - exactly what you want. But coming back means you are fighting those same trades.

However, there is a way to get back which usually does not involve too much pain. Using the clockwise circulation pattern around the high center, the sailing route is to head north or northeast from the Islands, and then follow the circulation pattern, still clockwise, around the top of the high. You have anywhere from 400 to 900 miles of close reaching and beating, and then somewhere around 35 to 38 degrees North latitude, you turn right and head for the coast.

If your destination is the Pacific Northwest, or Alaska, this is great, essentially a downwind passage. But to Southern California or Mexico, it adds quite a few miles. For our purposes we are assuming we have 2500 miles to cover on the way back.

As the year winds down towards winter, the jet stream begins to move south, bringing with it that lovely winter weather for the Northern hemisphere. The jet stream pushes the high south. This makes the passage east from Hawaii a lot easier. Even better, big low pressure systems with associated fronts often drop down close to the latitude of Hawaii, bringing westerly quadrant winds, and completely squashing the high.

Wind Horse has the ability to head straight back to the mainland, against the trades, following a great circle route. However, this is hard on fuel consumption, and even harder on the crew (the boat doesn't care). If possible, we would like to use the traditional sailboat approach: work our way north or northeast to the high's center, and then head west.

The problem right now is that the jet stream has been hanging out at latitudes where it should only be found in the summer. This allows the high to be in a summer position as well. The end result is strong trades, and the need to head really far north after leaving Hawaii before finding the windless center. Not what we want.

On the other hand, we're anxious to get home, and we do have the ability to do this the hard way, if we have to.

Above is the 500mb level 96-hour forecast. Notice the zonal (unstable) flow from west to east. There are also a series of short wave troughs signified by the dashed lines running from the pole towards the equator. Looking at this type of chart would indicate a big surface low was about to kick off.

This is the same time frame for the surface forecast. You can see the low starting to develop up in the well to the west of the the Aleutian Islands, with another well formed in the Gulf of Alaska. The high is being pushed south, and is losing its shape. Where the center has been up around 1030mb, it is shown here down to 1024mb.

This shows just the area between Hawaii (bottom left corner) and the mainland. Notice the depression in the north coming off one of those short wave troughs shown on the 500mb chart. One of the key things here is the center of the high shown moving to the east, with a second center about 600 miles north of Hawaii.

This type of scenario could make for an easy trip home.

The image above is from the GFS weather model for eight days from now. Of course, at this far in the future you have to take this with a grain of salt. However, it shows an intense high pressure system moving down from a position well to the northwest of here. We would not want to deal with this. On the other hand, the breeze between here and the mainland is light and variable, an ideal situation. What this says to us is that three days from now might be a good time to depart - unless we want to hang out for another couple of weeks, which we would rather avoid.

Rick Shema is a weather router based in Honolulu. He provides routing services for cruisers, racers, and commercial operators (weatherguy.com). Since this is his back yard, we've been using Rick's expertise to guide us back towards the mainland, and discuss the various options. The following comments are based on Rick's observations from yesterday.

Weather Summary as of 07October1200Z (0200 HST)

Today's weather pattern shows strong high pressure north of the Hawaiian
Islands centered near 34N 156W at 1031mb. Ridging from the high extends
throughout the eastern and central Pacific Ocean (EPAC). Wind and sea
conditions this morning at Buoy #1 (51001) were measured easterly winds
19-23kts with gusts to 29, significant sea heights 9-10 ft at 9-10 second
period. Average height of highest 10% of these waves is calculated at
12-13ft. Buoy #1 is located about 170nm WNW of Kauai Island near 23 26N 162
12W. This position is currently in similar trade wind air mass as Oahu and
waters north.

The polar front is to the north of the high extending from a triple point
low near 49N 154W roughly oriented east-west along about 40N. The front is
moving south east.

So far this season, there have been an average number of extratropical lows
transiting from western Pacific into the Gulf of Alaska. These lows have
been contained mostly north of 50N due to the presence of the high pressure
system anchored by an upper level ridge in EPAC. The U/L ridge axis has been
moving east to west as the jet stream remains north of 40N. Normally for
October, we would expect the ridge to begin weakening and begin moving south
east towards its winter time position near 30N 135W. Instead, a summertime
regime is maintained. This should be the case for the next week or so. I
would expect the ridge to begin weakening near the end of October.

At the surface, high pressure centers have been migrating east-west along
35N or so. Expect the current high center to begin weakening as the cold
front moves south east next 24-48hrs. This should relax the high, lighten
the trade winds in vicinity of Hawaii and more importantly reduce the sea
state to about 6-8 ft (Hs).

There are some consistent differences between GFS and NOGAPS model runs
these past few cycles. NOGAPS weakens the high more than GFS by about 3 mb
over the next 48hrs and moves the center further east in advance of the cold
front. Also, GFS dissipates the cold front quicker than NOGAPS. Would tend
to go with NOGAPS due to recent verification data. Therefore, would expect
the cold front to extend southwest through 40N 145W to 32N 162W by Sunday
morning. This should provide a departure window before
the next 1030mb high pressure builds in from the west behind the cold front
and increases the trade wind conditions on Wednesday /Thursday timeframe.

If we were on one of our sailboats we'd probably wait a couple of more weeks for the high to move south on a more permanent basis. But Wind Horse has the ability to deal with what we are looking at, even if we end up having to beat more than anticipated. So we are inclined to depart in the next few days. We'll be watching the weather models, looking at what the Marine Prediction Center is saying, talking with Rick, and checking the local conditions with the sea buoy reports. If things look the same in a couple of days, we'll probably put to sea.