Contrary to popular belief, the weather in California-much like its geography is not created equal. That said Monterey Bay suffers from the reputation for being one of the coldest, overcast and at times wettest areas in the state. A trip to Monterey Bay mean planning accordingly in terms of what wear. Sweatshirts, jackets, and long pants are a must-often even in the summer. The area tends to not enjoy a lot of sunshine as there is usually a persistent layer of fog that hangs over the coast (although it is usually sunny and much warmer if you travel inland just a few miles to either Carmel Valley or Salinas.
Summer is the best time to see Monterey Bay. The weather is usually dry and the entire state of California almost never sees any rain during this time. However the area often is socked in during the summer by a thick fog (that often retreats in the winter).
Although fog isn't as prominent as it is in the summer, Monterey Bay tends to get several slow storm systems that are heavy with moisture. The area often gets storms that last weeks dumping enough rain to shut Highway One down for a few days. However it should also be noted that every few years the region experiences a dry period during winter with little or no rain. Statistically speaking it rains more often than not during winter but if planning trip during this time would be wise to check to see what rainfall has been-perhaps that is the year Monterey Bay is on the dryer side.