The 2012 eastern Pacific and Atlantic hurricane seasons has begun

Advertisment
  • Hurricanes are enormous weather systems, which are typically about 300 miles wide and they take energy from the warm tropical oceans over which they form.

    A map showing the track of Tropical Storm Alberto, which was the first storm of the 2012 Atlantic hurricane season. Source:NOAA

    Hurricanes bring heavy rain and strong winds, which can lead to flooding.

    Hurricane can sometimes spawn tornadoes. It is frequently reported that the north-eastern quadrant of a hurricane system is the most dangerous in terms of storm surge, winds and tornadoes.

    Hurricanes can sometimes track across the Atlantic towards the UK bringing heavy rain and strong winds. In September 2011, the remnants of hurricane Katia brought a large swell along the coasts of south-west England. Source: Tim Ireland/PA Archive/Press Association Images

  • The 2012 eastern Pacific and Atlantic hurricane seasons has begun
    19.05.2012 12:12


    The formation of Tropical Storm Aletta to the south-southwest of Mexico on 14th May 2012 marked the unofficial start of the 2012 eastern Pacific hurricane season. The official start to the 2012 eastern Pacific hurricane season was a day later on 15th May.


    Aletta is only the third tropical storm that has formed prior to the official start of the eastern Pacific hurricane season since 1949. The formation of Tropical Storm Aletta also ended a 41 day run without a tropical storm anywhere in the world, which is said by some sources to be the longest period without a tropical storm in at least 70 years.

    The 2012 Atlantic hurricane season also got underway early when Tropical Storm Alberto formed off the coast of South Carolina late on Saturday 19th May; ahead of the official start of the season on 1st June. Alberto is the earliest-forming Atlantic tropical storm since 2003 when Tropical Storm Ana formed five weeks prior to the official start of the hurricane season. The formation of Tropical Storm Alberto means this is the first time tropical storms have formed before the official start of the hurricane seasons in both the eastern Pacific and Atlantic oceans.

    With the early starts to both the Atlantic and Eastern Pacific hurricane seasons, and with the 2012 Central Pacific season scheduled to start on 1st June, it is an ideal time to start looking at why hurricanes form and what the preseason forecasts are indicating for the 2012 Atlantic hurricane season. 

    Hurricanes form between the Tropics of Cancer and Capricorn and require three main features to be in place for formation to occur:

    •    Warm tropical oceans, with sea surface temperatures exceeding 27C (81F)
    •    Abundant moisture in the air
    •    Light winds in the atmosphere aloft (low wind shear).

    A hurricane is a type of tropical cyclone and in the northern hemisphere a cyclone’s winds near to the Earth’s surface rotate in an anti-clockwise direction. There are three stages in the life cycle of a hurricane:

    1.    Tropical Depression – an organised system of thunderstorms with maximum sustained winds of 38mph or less.
    2.    Tropical Storm – an organised system of severe thunderstorms with maximum sustained winds of 39-79mph.
    3.    Hurricane – An intense tropical weather system of strong thunderstorms with maximum sustained winds of 74mph or over.

    Once hurricanes are formed they take energy from the warm tropical oceans over which they have formed, and so whilst a hurricane remains over the warm oceans it will often continue to strengthen. However, once a hurricane moves across an area of colder water or across the land it will weaken as there is no longer any energy to fuel the tropical system. Hurricanes are enormous weather systems which are typically about 300 miles wide, but they can be as much as 430 miles wide. At the centre of each hurricane is an eye, in which the winds are relatively calm and the weather can be clear; the eye tends to be approximately 20-40 miles wide.

    The strength of a hurricane is defined by the Saffir-Simpson Hurricane Scale, with category 1 hurricanes being the weakest (wind speeds of 74-95mph) and category 5 hurricanes the strongest (winds greater than 155mph). It is frequently reported that the north-eastern quadrant of a hurricane system is the most dangerous in terms of storm surge, winds and tornadoes.

    Forecasts for the 2012 Atlantic hurricane season call for about 11 named storms, 6 hurricanes and 2 major hurricanes (Category 3 or higher on the Saffir-Simpson Scale). This is slightly below average, with a long-term average from 1950-2011 of 12 named storms, 7 hurricanes and 3 major hurricanes.

    The reasons for this slightly below average prediction in activity are that the North Atlantic ocean temperatures are expected to be a little lower this year, and there is a trend towards El Niño conditions which suggest a reduction in tropical cyclone activity. However, it is important to note that these predictions are for numbers of storms forming anywhere within the Atlantic and not the number of storms predicted to make landfall in the United States. This preseason hurricane forecast also comes after two very active hurricane seasons in 2010 and 2011.

    The accuracy of these forecasts is unknown and only time will tell. We will have to wait until the end of the hurricane season on 30th November before we know how many hurricanes have occurred within the Atlantic Ocean during the 2012 season.

    By: Gemma Plumb