Meteorological and Oceanographic Conditions During the 1970 Bermuda Yacht Race

Abstract

Analysis of conventional data and of information provided by a number of the competing skippers yields an unusually detailed picture of environmental conditions during the Newport, R.I.–Bermuda Yacht Race in June 1970. Sea-surface temperature data indicate the presence of a warm meander of the Gulf Stream just west of the rhumb-line course, a position intermediate between that of a warm meander to the west in May disclosed by bathythermograph observations from the RMS Franconia and that of a warm eddy to the east in August found by a Naval Oceanographic Office survey. The fleet was harassed by two groups of severe thunder-squalls during the night of June 21–22, in the vicinity of the warm meander. Even the anomalously high sea-surface temperatures, however, were cool relative to the air in which the thunderstorms were rooted. The storms originated in the Chesapeake Bay area during the day on June 21, and they appeared, surprisingly, to gain intensity over the ocean after being cut off from their surface source of warmth and moisture. Offshore forecasts for June 21–22 took no specific account of the presence of the severe thunderstorm systems. On June 25, part of the fleet experienced an unexpected southerly gale just northwest of Bermuda. From the yacht data, it is found that the gale was attributable to a small cyclone that formed in an old frontal cloud band and moved northeastward, remaining undetected by the conventional data network throughout its life history. Analysis of the surface wind field suggests that baroclinic effects played only a minor role in the behavior of this cyclone, which at least in some respects resembled a tropical cyclone. Study of the forecasts available at the time indicate that in neither case did small-scale convective activity have a significant direct effect upon the larger scales of motion.