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NA Hurricane Outlook 2009

by on Sunday 9th August, 2009   12619 Views

Atlantic Seasonal Overview

The NOAA have just released a revised forecast for the 2009 Hurricane season and with the critical August to October period (typically the most active time of the year) about to begin we thought we’d give a brief overview of what it means for surfers.

Most of us watching keenly for the chances of a decent surf producing Tropical system won’t need to be told that we’re already experiencing a less than active year. While it’s relatively early none the less the last two years had already delivered several named storms by August with last year both Bertha and Dolly reaching Hurricane status in July and deliving quality surf.

So it’ll come as no surprise, therefore, to hear that the NOAA general forecast for the season is for lower than normal activity. We’re moving into an increasingly strong El Nino cycle - this climate phenomena involves a change in the pattern of sea temperatures in the Pacific with warmer than average water in the coastal regions of Central and Southern America and also has an affect on the global climate. With respect to the Atlantic it means a generally pronounced easterly wind flow in the upper atmosphere which tends to mean that the tropical storms forming over warm water off the coast of Africa get disrupted in their early stages - in short it reduces the chances of an active season.

So altogether taking into effect the mid term trend (which is for more hurricanes than average since 1995), the Alantic sea temperature (which is warmer than average and helps the development of storms) but moderated by the effects of El Nino the NOAA are reducing their outlook to most likely a below average year for Tropical Storms. For us it means that while we might have become accustomed over the last few years to a succession of surf producing systems througout the season this year might buck that trend.

The NOAA are keen to stress that those affected by the devastating effects of landfall hurricanes don’t become complacent and likewise for surfers a below average season certainly doesn’t preclude the formation of significant storms that could produce excellent surf conditions, it just means the chances of a lot of these systems over the season is lower than normal for 2009.

Hurricane Surf Forecast Problems

As surfers we’ve become increasingly dependant on computer generated swell forecast models (at Magicseaweed we hope we’ve been a part of that process) but these same models do present us with a problem come hurricane season that we think is worth explaining here.

The ‘model’ is simply a computer program that breaks the globe down into a big grid. It then looks at the wind strength in each grid square and calculates the height of the waves produced. It’s a little more complex than that might sound but, long story short, the numbers spat out of this process are the the basis for the ones you get here on MSW and elsewhere as a local surf forecast. It’s remarkably accurate (for which we can take no credit - this isn’t a propaganda piece!!! - This computer software has been developed over decades by the NOAA) for normal pressure systems however there’s a flaw in this for Tropical storms.

To calculate the forecast for the whole globe (essential as it’s a global system we’re dealing with) the model, as we said, breaks the surface of the sea down into ‘grid squares’ about 30 miles across. With the average decent surf producing storm some hundreds of miles across this allows us to accurately forecast the swell across open ocean.

For tropical storms this grid size can be a problem. Bear in mind that the size of waves a storm produces are a combination of it’s strength, how long it blows for, and the size of the area over which it blows and you’ll understand that a tropical storm can be very very small, but very very strong and produce considerable surf, just as a normal storm can be much weaker but much bigger to produce waves the same size. However our ‘model grid’ is large enough that even a powerful system just tens of miles across can effectively get ‘lost’ in the cracks - the forecast simply can’t see something this small as clearly as it needs to. This can tend to mean that the waves produced from these kind of storms get undercalled here on MSW and elsewhere.

We do use a special model designed specifically for Hurricane season that aims to combat this - and the results are a definite improvement but it’s worth a little caution none the less.

Our New NA Hurricane Forecast

With this in mind we’re going to run a North Atlantic Hurricance forecast straight into your local beach page here on MSW over the coming season - giving you an in depth but easy to read guide to every potential surf producing storm as it starts to form.

Warm Water Signals El Nino Formation © 2014 NOAA/NWS

 

Highly active season last year overview © 2014 NOAA/NHC

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