Neap-spring tidal patterns in Atlantic tropical cyclones

Heat content of subsurface ocean waters is thought to influence tropical cyclone intensification, but little is known about short-term temporal variations in this influence. I examined long term mooring data from three sites in the North Atlantic, and cyclone best track wind speeds, for evidence that neap-spring tidal temperature fluctuations below the surface might affect cyclone intensification. Temperatures at individual depths between 35-150 m at all three sites showed greater day-to-day fluctuation than nearer the surface, with daily changes of ± 0.40C occurring on as many as 38% of days at one site, and at least one depth at all sites averaging a weekly temperature range of = 0.70C. Thus, the ability of a storm to cool its own sea-surface environment through mixing might vary over short time scales. Temperatures at all three moorings were dominated by peaks near the new moon, but these patterns were not statistically significant and encompassed variations of only 0.1-0.20C across the lunar cycle. Basin-wide storm records did show strong association with the spring-neap cycle. From 1950-2007 both the frequency of hurricane-force wind observations and mean tropical cyclone wind speeds varied substantially across the lunar synodic cycle, both peaking ~7 d after the new moon. Rapid intensification events started more frequently near the full and (especially) new moons, the new moon peak matching the dominant peak of sub-surface temperature at the mooring sites.