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Boating Weather for the Long Haul

A cruising couple downloads and analyzes GRIB files to find the best route across the South Pacific.
Boating Safety

Just past our halfway point
October 5, 31°27.9’S, 101°02.2’W

>> Synopsis: We’ve started edging south in the band of northerly winds between a high to the southeast of us (center pressure 1028 millibars) and a low to the southwest (center pressure 1008 millibars). (See 10/05 1800 (12 hours).) As the low (center pressure 1010 millibars) continues to the west, it will bring a moderate band of westerly winds along our course, between 30 degrees S and 36 degrees S for 48 hours. (See 10/07 0600 (48 hours).) As it moves off, a high (center pressure 1023 millibars) approaches from northwest of our position and ridges down between the low moving away from us and the next low approaching from the west. this ridge will bring us light and variable winds while preventing the westerly winds from the next low-pressure system from actually reaching us. (See 10/10 0600 (120 hours).)

>> Analysis: We’re now a bit over halfway to Canal de Chacao, and we’ve made half of our easting, but we’ve only made about a third of our southing. We need to start working our way south, and we’d like to get south quickly enough to reach the band of 20-knot westerly winds just to the north of the low. once again, the forecast for the last three days of the period is very mushy and has been changing daily, so we’ll take the risk of ending up in the middle of the high-pressure ridge forecast to fill in October 10. We’ll see what develops after the low moves off and adjust our plans accordingly.

>> Strategy: Sail southeast along the great-circle course to Canal de Chacao (106 degrees magnetic). For the next 48 hours, expect northwest winds (shifting to the west) at less than 20 knots.

>> Actual: The weather we experienced wasn’t as forecast. the low moved more quickly north and east than expected, bringing us a frontal passage with northwest winds of more than 30 knots shifting to west and then southwest. Southwest winds of 20 to 25 knots lasted for another 24 hours, taking us through October 7. The actual weather gave us fast downwind sailing, and we made good 175 miles per day toward our destination on October 6 and 7. The low-pressure system then slowed, and we were able to make another 165 nautical miles in the southerly flow behind it on October 8.

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