Clouds gives the low-down on San Fran’s big breeze

The America’s Cup World Series fleet can expect more strong breeze when racing starts this week.

The strong w-sw sea breeze that caused the damage on Saturday  moderated early in the week, but by Thursday – first race day for Dean Barker and crew – it will be back to its boat-breaking best.

Emirates Team New Zealand meteorologist Roger (Clouds) Badham says that at this time of the year San Francisco weather comes in three to five day cycles. Locals say the best weather is in September/October.

“The breeze is stronger at the beginning of the cycle and moderates towards the end.  The primary driver is the cold current (about 10-11deg C) that comes down the coast.

At night, cold and damp air brings fog into low-lying areas of the harbour.  Further inland, unaffected by the fog, the land heats rapidly during the day bringing on the sea breeze which affects the harbour east of the Golden Gate bridge.

“West of the Golden Gate bridge there is no sea breeze,” Clouds says.

Over three-four days, the layer of cloud thickens and settles as fog further inland. This limits the heating effect during the day and, consequently, the sea breeze is not so strong.”

‘We will see this over the next couple of days; it will be slightly cooler and the breeze slightly less dynamic.”

The breeze is not constant across the bay. On the northern side its mean speed is typically stronger -20 knots plus. On the southern shore may be 15 – 20 knots but the gusts will equal those to the north.

And the temperatures?  Around the harbour perhaps 15-16 degrees; in the eastern suburbs of San Francisco it is hot – 30 plus degrees – creating ideal conditions for the sea breeze to develop.