As we settle into the doldrums of summer, I ponder this most bittersweet of seasons. Sure, the water ís warm, beaches are littered with bronzed ESM girls, and there ís a party every night, but the swell activity just doesn't match up to rest of the year. There is, however, one light of hope at the end of the hour: your Tropical Update, courtesy of the Weather Channel. Thatís right folks, itís hurricane season!!
Perhaps we should start by defining the various tropical phenomena for the extreme novices. Hurricane season runs from June 1 to November 30 and marks the time where intense, tropical low pressure systems develop in the Atlantic basin. Fueled by warm water, these lows grow from tropical depressions to be categorized as a tropical storm once the speeds reach 39 mph, at which point they are given a name. If the named storm grows to 74 mph or above, it is classified as a hurricane, which are divided into five categories depending on their severity (see figure A). These storms are revered by surfers for their ability to send epic swells, and feared by most everyone else for their ability to decimate coastal communities.
So what kind of season are we looking at? Well, according to my sources, Dr. William Gray (renowned tropical prediction expert from somewhere in Colorado) got so toasted on last year's prediction that he ís now working for the Psychic Friends Network. So, hereís my forecast, guaranteed to be 100% accurate or the next magazine ís FREE: in 2000 there will be hurricanes in the Atlantic basin. Yes, there will be hurricanes and the East Coast will get some classic swell--somewhere. Whenever that swell arrives, you're going to want to be there at the right time and place so let's examine exactly how to do that.
Just because hurricane season started on June 1 doesn't mean storms instantly start marching up the coast. So, in this issue we'll discuss the factors positive for hurricane development, and how to roughly gauge where the strongest swell will be heading. Next issue weíll factor in the specifics of swell generation and its direction, just in time for the meat of the season.
First, it ís important to emphasize that quality, swell-producing storms rarely form in the first half of the season. To get an idea of when the season should really start to fire up, watch for when the National Hurricane Center starts numbering these tropical depressions. (When tropical thunderstorm activity starts showing signs of development favorable for a hurricane, they are designated as tropical depressions and assigned a number.) Occasionally, the first tropical depression develops into a full-blown hurricane, but this is rare. In fact, surfers should avoid getting too eager over these early summer storms because the water temperatures off of the US coast are often too cool to fuel such a hurricane. Of course, there are exceptions such as Hurricane Bertha, which blanketed the right coast with pristine swell in early July 1996. However, Bertha was the first storm since 1966 to reach such strength so early in the year. The point is: most of our good hurricane swell comes during the second half of the season, usually beginning in August. By then the water is warm enough everywhere along the Eastern seaboard that storms can form not only in the Intertropical Convergence Zone or ITCZ--a fancy name for the place in the tropics where most storms develop--but can also pop up almost instantly from off of the Florida Coast all the way up to the Outer Banks.
So why all this attention on water temperature? Well, hurricanes need water that is at least 80* F in order to develop. This is by far the most important and essential ingredient in tropical storm formation. The other important factors to watch for while your eyes are glued to the Weather Channel all season concern ìair pressure aloftî and ìwind shear.î High pressure aloft, which means high pressure in the upper atmosphere, is positive for storm development. On the other hand, if you hear the weather person say that there is an upper level low in the area where you are looking for storm formation, then forget about it--at least for a couple of days until conditions have a chance to change. You also want to beware of excessive wind shear, which occurs when the upper level winds are too strong to allow the storm to develop. Wind shear can also severely weaken existing storms. Translation: wind shear = bad. Thanks to that pesky brat, El Nino, the Atlantic saw excessive wind shear last season and just about every storm that tried to develop got torn to shreds. Hence, we had a crappy season. In the future, if you ever hear that one of these phenomena is on its way, get outta Dodge--the Right Coast instantly becomes the wrong coast during heavy El Nino summers.
While the ITCZ is where most hurricanes fully materialize, the true roots of our favorite storms are more or less in Africa. Granted, storm development off the US coast does occur and can produce great systems, but the bulk of the activity stems from West African Sahel region. During the summer, check out a satellite image of Africa and if there is a lot of thunderstorm activity in West Africa, that is a good sign. These same West Africa rains eventually cruise west off of the African coast into the Atlantic to become the patches of cloudiness and thunderstorm activity that meteorologists refer to as tropical waves. Once the air pressure begins to drop, these tropical waves may spawn tropical depressions. And if the water is warm (over 80* F) and the upper level atmospheric conditions can be considered favorable (high pressure and minimal wind shear), then we have the ingredients necessary for further development.
Once the weather man shows a picture of brilliantly white thunderstorms twisting counter-clockwise, that means something worthwhile may be brewing. The jewel to look for here is falling air pressure. Normal atmospheric air pressure is 1013 millibars. A tropical storm will start to show a little balls once it gets under 990 mb and the further it drops, the better. The real monsters get down as low as the 930ís and some incredibly intense storms have sunk to the 900ís. With a little luck, the pressure falls, winds crank up to 39 mph, and voila: we officially have a named tropical storm. At this point, natureís will shall decide whether or not we get a hurricane or not, but if the favorable conditions persist, the chances of this storm growing into a hurricane are quite good. Regardless, a storm of this magnitude is enough to produce swell so let the tracking begin.
Hurricanes are steered by whatever other surrounding pressure systems it comes in contact with. Way back in article #1 (Vol. 7, Iss. #47) we talked about high and low pressure and their respective circulation. A quick review reminds us that high pressure systems rotate clockwise and low pressure systems rotate counter-clockwise. Once again, [this] is very important as these systems act in part as the steering currents for tropical systems. Low pressure systems suck air inward toward their center and can draw in another storm or merge with the system with varying results. A cold-core system may weaken the storm in question; a second, warmer tropical system may strengthen the storm in question; however, the reverse has been known to happen as well.
More importantly, high pressure systems are the muscle when it comes to steering a hurricane, because the two pressure systems oppose each other, in effect allowing the high to repel the low in a general direction. Often the size of the Bermuda High--a large high pressure system that tends to sit over Bermuda and gives Florida three months of onshore winds and New England perfect offshores all summer--determines a hurricaneís track and itís proximity to the US coast. The peak season storms emanating from the Cape Verdes generally take a clockwise track between the coast and around the Bermuda high. If the Bermuda High is strong, the storm may crash into the USA, such as Fran did in 1995. When a hurricane does hit land, the best surf is usually to the left of the track where the winds are offshore. When the Bermuda High is weak, the storm will curve away from the coast. In this case, a few days of moderate to strong swell are possible, provided the storm doesnít move away too quickly.
Once you have an idea of where you think the storm may go and youíve got it plotted out on your nifty tracking chart, letís figure out what kind of swell weíre looking at. First off, determine exactly which direction the hurricane is traveling in (The stormís direction is standard info provided with any tropical update.) Once you know the direction you can determine where the strongest wind field is. The strongest part of a hurricane or tropical storm (letís use the term hurricane from now on because itís easier and sounds better) is on the side which lies to the right of its path (see figure B). So if a storm is heading due north, the strongest winds will occur on the right or east side of the hurricane and circulate counter clockwise around the eye. Consequently, the upper-right quadrant is sending the strongest swell; however, not all hurricanes follow the normal tracks. If a hurricane gets caught where winds aloft are weak, it may stall or perform a loop. In this situation, considerable swell is generated from all sides of the storm. The radiating wave pattern is similar to what you see if you drop a rock in a puddle. Although lengthy hurricane stalls arenít common, a few slow movers have produced a week or more of macking surf up and down the East Coast--does anybody remember 1995 ís premiere wave philanthropist, Felix?
If everything falls into place and we get a storm which has sizable wind field, we know the swellís general direction and are ready to start doing some math and find out when waves are going to arrive at our local beach (or, more importantly, somewhere else). To stay on top of hurricane activity, go to the National Hurricane Center's Tropical Prediction Homepage at http://www.nhc.noaa.gov/ Keep in mind that a hurricane may not produce swell due to a variety of factors--especially fetch--but to really figure out the details youíll have to pick up the next issue of ESM for the Cult of Climatologyís look at the physics of waves, swell movement, and all that good stuff. Until then, pray that Huracan may be kind and juicy.
Here are Surf Forcasting Link's offered by Darren Saletta in his seven article Eastern Surfing Magazine series
entitled "The Cult of Climatology".