Hurricane season hotting up

  • Tropical Storm Isaac, looming over Haiti and the Dominican Republic with Cuba next in line. Image: NOAA/NASA GOES Project

    A wider view of the western hemisphere, showing Tropical Storm Isaac in the Caribbean and Tropical Depression Joyce, due to become a tropical storm again as it turns N then NE, coming close to Bermuda. A tropical wave in the eastern Atlantic will slowly develop as it moves westwards. Image: NOAA/NASA GOES Project

    A suite of model forecasts, showing that most agree on Isaac moving NNW across the eastern Gulf of Mexico, close to Florida. Image courtesy of University of Wisconsin-Milwaukee

    Models agree quite closely about where Joyce will go as well. Image courtesy of University of Wisconsin-Milwaukee

  • Hurricane season hotting up
    24.08.2012 13:02


    If anybody is flying away from these shores to escape changeable Bank Holiday weather they had better not be heading for Florida, the Gulf Coast or the northern Caribbean

    The Atlantic hurricane season has started to reach its peak, and Tropical Storm Isaac is being very carefully and fearfully watched. It is on the verge reaching hurricane strength as it moves north-westwards to the south of
    Puerto Rico and approaches the island of Hispaniola. Its centre is most likely cross Haiti or the southern and western Dominican Republic during Friday evening and night.

    The tracks of hurricanes and typhoons are notoriously fickle and difficult to forecast but meteorologists have access to a suite of models that have become increasingly reliable during the past few years.

    Using these as guidance they can plot the hurricane’s most likely course but always with a “cone of uncertainty” that widens the further ahead they are trying to forecast. As it happens the various models have fairly close agreement on where Isaac will go, and this is reflected in forecasts from the National Hurricane Centre’s meteorologists. They advise that after crossing Cuba a gradual curve to a north-northwesterly direction should bring it close to or across Florida’s Gulf of Mexico coast early next week, perhaps crossing the Keys first then heading towards the Gulf coast between Louisiana and the Florida Panhandle.

    Clearly, then, vast numbers of people across the northern Caribbean and in and around the Gulf of Mexico are going to be hammered by fierce winds, torrential rain, floods and, at least in the case of Cuba, the Dominican Republic and Haiti, the risk of landslides. Storm surges will batter some coasts with tumultuous waves.

    Further out in the Atlantic, to the east of Isaac, Tropical Storm Joyce has just been named, deepening from a north-westwards moving tropical depression during Thursday. This seems to pose less of a threat, with forecasts tending to agree that it should curve away on north then north-easterly path before reaching either the Caribbean or the Eastern Seaboard, and that it might not quite achieve hurricane strength.

    Even farther east a tropical wave has developed in the “nursery” of hurricanes, near the Cape Verde Islands in the very warm waters off western Africa. Although there is little chance of any significant development in the next couple of days it is likely to strengthen as it continues westwards across the tropical Atlantic.

    Why have these storms suddenly started to fire up? After all the “hurricane season” begins at the start of summer.

    Firstly, despite a nominal season of early June to late November the peak is more often than not from late August through September. Hurricanes need the duel fuel of moisture and warmth to thrive, and the tropical Atlantic is at its warmest during this time.

    Secondly, the tropical Pacific Ocean is warming, which means that the two-year La Niña episode has just ended. Interactions between the ocean and the atmosphere mean that hurricane activity tends to be amplified n the Atlantic during La Niña while subdued in the Pacific, and vice-versa. We might expect fewer Atlantic hurricanes on the face of it but the effect is not necessarily immediate, and the surface waters of the tropical Atlantic are much warmer than average at the moment.

    Whether or not hurricanes are likely to make landfall is open to conjecture; but the niceties of that research will be irrelevant to those boarding up their houses in Isaac’s path.

    By: Stephen Davenport