… plenty storm soon come

Last week, both the Colorado State University hurricane team (CSU)and the U.S. National Oceanic and Atmospheric Administration (NOAA) updated their forecasts for this year’s tropical storm season.  Both of them still expect “well above average” activity.  The next few months are likely to be very busy -- with a slow start to the season, getting to the forecast total will mean a named storm almost every week...

For part of June and most of July, a heavy blanket of hot dry dusty Saharan air covered the tropical Atlantic.  The regular parade of tropical waves that started across the Atlantic – at least ninety of them so far – have been trapped in this Saharan air layer.  Only three became named storms, and most have amounted to little more than rain squalls and thunder.

As the table shows, CSU has slightly increased its forecast while NOAA has trimmed the top end of its range. They have ended up in the same place, forecasting about twice the average level of activity.  The forecasts of Accumulated Cyclone Energy (a product of storm days and wind speed) range from 85% (CSU) to 115% (NOAA) above the historical median.

The elements that produced big forecasts in the spring have all developed as expected.  A La Nina (cool Pacific current) has developed over the last month.  Combined with low sea level air pressure in the tropical Atlantic, this means weak trade winds and less wind shear to pull storms apart when they reach the Caribbean.  Sea surface temperatures are still at record high levels, and this helps developing storms to gain strength.

CSU has developed a specific forecast for the Caribbean basin.  The team is 99% certain that at least one hurricane will track through the Caribbean this year, and there is a 64% chance it will be a big one.  (Historically, the average probability of this is 42%.)  One reason is the appearance in July of unusual upper-level east winds over North Africa.  These winds, usually associated with a heavy African monsoon, suggest that there could be a lot less Saharan dust to protect us for the rest of the storm season.  (As we went to press, the Saharan Air Layer map showed the Caribbean almost clear of dust, and only scattered wisps beyond the mid-Atlantic.)

Even if no storm hits Jamaica, there is a real threat from the heavy rains on the edge of a hurricane going somewhere else.  The rain that’s been falling so regularly since April has ended our “long dry”.  It’s also left the soil in most areas well soaked and the rivers full.  A heavy downpour with a bit of wind will see trees falling over because their roots won’t hold, and rivers bursting their banks.

Whatever the forecast, it only takes one storm to put your life and property in danger.  It’s not too late to make a plan and be prepared.  A little effort now could save a lot of misery later.