PANAMA CITY — This weekend’s weather forecast holds a surprise: 10 knot winds with gusts up to 16 knots and an invasion of Vipers in St. Andrew Bay by early Saturday afternoon. The Vipers, all the way from New Zealand, are a relatively new phenomena in the bay, their appearances growing since the Gulf Yachting Association switched to the faster, more-vibrant vessel as the official boat of its annual regatta series.