Geography of Bermuda - Climate

Climate

Contrary to common belief, Bermuda is not located within the tropics, but within the Middle latitudes, or Temperate Zone. The warm temperate, or subtropical (the term favoured by the tourism industry, although Bermuda's weather is not actually characteristic of the Subtropics, any more than of the tropics—the subtropics is not so much a geographical area as a collective term for areas with subtropical climates. Bermuda's climate is more truthfully described as Warm Temperate or Oceanic), weather is influenced by the Arctic air mass, the Westerlies, and the Gulf Stream. Bermuda has a very humid climate and, as a result, the summer-time heat index can be very high, even when the actual temperature seems moderate. In fact, the highs reached even during summer days are usually as much as 10 °F (5.6 °C) to 20 °F (11.1 °C) lower than in areas farther to the north, including New York, Chicago, and areas of Alaska. Winter temperatures can be very chilly, and the powerful winds and heavy rain mean that the felt temperature can fall below freezing, even though the actual temperature may rarely drop much below 10 °C (50 °F). There has been a general warming trend observed, however, since the late 1980s. Freezing weather has not been recorded since the 19th century, although hail is common in the winter.

Of the two dominating, and counter-acting weather effects over Bermuda, one may be termed regional, whereas the other is localised. The first of these results from the regular separation of large volumes of the Arctic air mass over the Canadian plains. With the prevailing wind direction in the Northern Hemisphere being from the West, this cold, dry air sweeps east, and southward across the eastern half of the United States, before crossing over the Gulf Stream to reach Bermuda (hence Bermudians usually obtain a two-or-three day warning of the approach of bad weather by watching the weather reports of the Atlantic Seaboard). From September through June, and especially during the winter and spring, the cold fronts of these advancing air masses sweep powerfully across Bermuda, preceded by two or three days of progressively stormier, wetter, and more overcast weather. Once the Fronts pass, they leave cold, dry air, and clear skies behind them. The localised effect known as the Bermuda High, warm, high-pressure air, fuelled by the heat of the Gulf Stream, rebuilds its strength for a few days before the advance of the next front causes progressively worsening weather. During the summer months, the Arctic air mass contracts, and its boundary moves north, resulting in weaker cold fronts that move more slowly, countered by a Bermuda High strengthened by the summer heat. The cold fronts are therefore further apart, and their effect less noticeable in Bermuda, although the weather can be very stormy even during relatively sunny summer days. Although the heavy, sustained rainfall associated with these fronts is largely absent during the summer, the relative humidity nears 100%, and dense, moving squalls frequently drop great quantities of water. It is not uncommon, during the summer, to ride on sunbaked roads, then round a corner to come suddenly on drenched and steaming tarmac where a squall has passed only minutes earlier. Consequently, although there is somewhat less rainfall during the summer months, Bermuda's rainfall remains relatively consistent throughout the year. The winter rainfall is most important, however, as, due to the lack of groundwater, this is the period when the islands' vegetation is able to store greater quantities of rainfall.

Bermuda's humidity moderates the extremes of temperatures reached (through the day, and through the year), with the difference between daily highs and low remaining fairly consistently about ten degrees Fahrenheit (although the arrival of a cold front can cause a more extreme temperature drop). The humidity also slows the rate at which the air gains and loses heat. The result is that, while Bermuda is generally warmer than the US North-East in Autumn and Winter, it is generally cooler in Spring and Summer, with temperatures reaching into the eighties in New York, or Chicago in late spring while Bermuda's temperature typically remains doggedly in the upper sixties, or low seventies. There is a distinct shift to summer weather, however, which usually occurs about the middle of June, and an almost as distinct shift back between late September and early October.