Bermuda to Chesapeake Passage: Reevaluating Weather Tactics with Surprising Forecast

1622 EST – The 48-hour forecast is a bit surprising, causing the Dashews to re-evaluate their tactics.

1622 EST. 32’43″N 65’45″W. The fax machine is chunking away. The 24-hour forecast looks about as expected. However, the 48-hour glance into the future looks like the computer/forecaster team have their days mixed. Monday, with a strong frontal passage and 30 knots of wind from the northeast, has become Sunday. The big low pressure system with the weak following high which is now over the Midwest appears to be accelerating. As our now land-cruising friend Dave Wyman says, “East Coast spring weather sucks!”

Here is where the weather tactics get interesting. Ahead of the front we’ll have favorable SW winds. Normally the rule is sail free and fast to the favorable shift. With the SW wind we can go faster and directly towards Norfolk. On the other hand, it looks like the period of SW winds will be short, after which we’ve got a starboard tack beat. Knowing this is coming, we probably should make distance to the north, so that when the stronger winds come onto starboard, we can sail freer than would otherwise be the case. The tricky part is timing. If you take the 24- and 48-hour forecasts as gospel, we should be about 200 miles from the mouth of the Chesapeake when the shift comes through. If that actually happens we’ll be crossing the Gulf Stream at the same time as the front, with the attendant wind shift. Maybe we should get out Surviving the Storm and have a read!

The GRIB file being used by the MaxSea routing software is now 12 hours older than these newest MPC predictions. Still, when we look back at its suggestions, they are valid for what’s coming (the routing algorithm says foot off to the SW wind, and then carry the SW wind N of the rhumb line to put some distance to windward “in the bank” for when shift comes through).

Our decision? Right now we’ll follow our own instincts, which parallel the routing software. So, we are making 10 knots over the bottom on a course 30 degrees to the left of the rhumb line as the wind continues to back towards the SW. The barometer peaked at 1022mb two hours ago and is now down to 1020 – so we’re through the middle of the high.

Tomorrow we’ll see what sort of signs we have in the sky about the approaching front, check the fax data, and the GRIB file. At that point we can decide to slow down a bit so as not to meet the front in the Gulf Stream or to push on to beat it across.

Posted by Steve Dashew  (May 11, 2001)

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