Interesting weather routing
Phil May and Andrea Twigg
Sun 14 Jul 2013 06:12
We left the Bahamas yesterday bound for the US (Annapolis or thereabouts). Tropical Storm Chantal had downgraded to a tropical wave and, although they were predicting a 30% chance of another storm forming in 24 to 48 hours from the residue, the new storm would be further west than we planned to be. Chantal was only 35 knots by the end anyway, so it did not seem like there was a huge amount of energy left in her. If we had delayed our departure then the predictions were for light winds for the next three days, so we would be faced with motoring for hundreds of miles.
The combination of Chantal and the Gulf Stream has made the weather routing interesting. If there was the prevailing south-easterly breeze we could just have headed over to the Florida coast, picked up the three knots of gulf stream and headed up the coast at 10 knots. Unfortunately Chantal messed up the wind, so the obvious route would have no wind initially and finish as a nasty wind against current situation.
The prediction was for a fairly narrow band of strong southerly wind to the east of our starting point, moving north and backing gradually over the next three days to become an easterly wind. The obvious route was to head eastward into the wind and then bear northward, following it round as it backed, hopefully maintaining a broad reach the whole way, as illustrated below.
This is exactly what we have done so far. The wind was initially strong, gusting up to 35 knots (as expected). We were just running downwind, with a double reefed main, enjoying the bursts of speed.
Looking ahead, the fly in the ointment is a large eddy in the Gulf Stream that lies directly on our path. This has the potential to give us a 2 to 3 knot counter-current for 100 miles. It is a bit too big to ride it around to the east, so we plan to head due north up its western side, sandwiched between it and the Gulf Stream. This forces us to do 50 miles close hauled, which is not ideal, but we also have the option of heading further north into the Gulf Stream proper, if the wind is fairly light and has no northerly component. It looks like that part of the Gulf Stream, flowing north-east, would be a maelstrom if it had a strong north-easterly breeze pushing against it.