The best indicator of the local conditions will be the forecast for the jet stream a week before the event. If the jet stream is further north in Canada, most of the regatta will have lighter breeze and clear, dry, and cool weather, with temperatures in the mid 60’s Fahrenheit. If the jet stream dips down below the Northeast corridor of the United States, racers can expect a low-pressure trough to move through the Marblehead area with fronts and at least one Nor’ Easter to impact the regatta at some point. We will likely see a variety of conditions during the 2018 J70 World Championships.
During the fall, Marblehead generally sees a weekly frontal passage similar to Miami in the winter. This could involve a low pressure depression from the Midwest with a warm front that is preceding a Northwest cold front featuring fresher land breezes one day which lighten on the following day.
Historically, a Nor’ Easter has influenced Mass Bay at least once during this week of September in 9 out of the past 10 years of data. This storm system usually lasts one or two days in varying severity with breezes from 12-25 knots and rainy choppy conditions. The second day is usually ligther.
Very commonly, a high pressure system out of the North or Northeast quadrant will feature lighter wind in the 5-12 knot range. This system will have decreased wave height and clear sunny days. This is what will happen if the jet stream is up north in Canada. The high moves very slowly and can hang around for 3 to 4 days, which may cause us to lose a day of racing due to light air.
During the summers in Marblehead, we will have light air but have the chance of the afternoon sea breeze. This is unlikely in late September and even less likely given warmer water temperatures the past few months.
Although Florence just hit the eastern seaboard, Massachusetts is not generally hit directly by a hurricane, but could be impacted by remnants of a tropical storm.
The location of the race course is primarily impacted by the currents in and out of Boston Harbor. There will be strong currents offshore but the most important factor impacting current will be whether or not there was large amounts of rainful prior to or during the event.
The data used in providing this local weather tips page is from the Mass Bay buoy which is about four to five miles northeast of the anticipated race course and is reported by the Northeast Regional Association of Coastal and Ocean Observing Systems.
The Nor’ Easter storm is well explained in this article by The Weather Channel here (this has some good graphics of what a Nor’Easter means for the area. As article mentions, a Nor’easter has influenced the conditions the last week of September in 9 out of the past 10 years.
Historic data found here.