Sunday, November 18, 2007

Ocean Science 101 (armchair forecasting!)

Hey guys,

In this post I will start my first installment of what I would like to call “Lazy Forecasting”. Basically I will offer some really simple tips and resources that will help you learn how to surf forecast without having to pay for some one else to do it.

Lazy Forecasting 101: How to get a reasonably accurate North Pacific forecast for California...(and here is the best part)…using only the weather satellite photo in the paper, and buoy readings.

Syllabus: I will cheat a little in this one because lets face it, print is pretty much dead, and the clarity of the images you can find directly from NOAA are far superior to what we would see in the paper…and don’t even get me started about the live buoy feeds that you can get directly from NOAA and Scripps…especially compared to the robots that read the info on the old buoy radio. Here is a good link to an animated satellite loop showing the NPAC photos from the last several hours.


1. Find yourself (physically not spiritually…but it is amazing how those go hand in hand). Find your location on the Paper’s sat photo.
2. Find the location of the storms in the North Pacific
3. Determine distance between you and the storm.
4. Estimate the storm strength.
5. Hurt your brain with math.
6. Wait for swell, drink, look at buoys, drink some more. Rinse/Repeat.
7. See buoys pick up swell.
8. Start Packing.

Materials – On NOAA Map + access to live buoy information.

OK this is a great map of the North Pacific, stolen from NOAA’s satellite group, It has a mix of infrared and visual data (the majority of the map is current showing infrared imagery.

It also has lat-long coordinates which is great for eye-balling storm fetch. Infrared is nice because it lets you see the particularly intense sections of the storm. When you are looking at a visual shot you can loose a lot of information in the cloud cover.

First Step: Determine if there are any storms in your swell window

1. Look for something that appears to be spinning. Now if looks like it is spinning counterclockwise then you have found a low pressure (aka a storm)

2. Look at it’s present location.
A. If it below the 50N Latitude (the bright red bar). then there is a good chance Northern California will get swell from this storm
B. If it is below the 45N Latitude then it is the swell window for both Northern and Central California
C. If it is below the green line then it is in the window for Southern California (along with Northern and Central California)

Things to remember
1. (L) Low pressures spin counter-clockwise in the northern hemisphere
2. (H) High Pressures spin clockwise in the northern hemisphere
3. The stronger the difference in pressure between the high and low the stronger the winds will be in that area
4. The more intense the winds the bigger the surf. The more intense the winds that are aimed at you the bigger the surf that you are going to get.

Getting Started

Step 1. Find Yourself – (Yeah you should probably get a map)

Step 2. Find your storm. Storms are caused by Low-pressure…so most weather maps will label storm centers with a giant “L”. Circle any L’s that look promising.

Step 3. Determine if there are any huge islands, counties, or continents in between you and the storm. (If the answer is yes…pick another storm). It the answer is no then try and determine distance between the two spots (either use the map scale…or just eyeball it…generally 1-degree of lat/lon is about 60 miles. So every 10 degrees is about 600 miles.

Step 4. Estimate wind speeds (this one is a little tricky) if you are seeing wide solid slabs of clouds it is probably not moving more than 10-20 knots. If the clouds look shredded...almost like popcorn then the wind is tearing it up with winds around 30-40 knots. Now if you see a swirling vortex of terror that is pulling in little snaking clouds and crushing them into oblivion and it is surrounded by a big swatch of those “popcorn” clouds that look like they are worshipping the center. Yeah that one would probably have about 50-70 knots winds and would be close to reaching hurricane force levels.

5. Swell once it is created by the storm travels through the ocean at fairly predictable speeds. We measure the speeds in what we call “swell period” or “swell interval”. The general rule of Thumb is that swell with 17 second periods can travel about 600-700 miles in 24 hours. Shorter swell periods travel slower and longer-periods travel faster. So for this exercise we have a storm 2400 miles away and the swell is traveling in 17 second periods. That means it would arrive at our location in about 4 days. (I think I need to lay down)

6. If the storm is properly positioned and setting up some fetch towards you and your spot then you can assume the swell is on the way. Now we just sit and wait.

Usually swells show up on time…sometimes they lag. Personally when they are really lagging I drink, check the buoys every five minutes, and swear at things. (but I have a lot of anti-social behaviors).

Then when the swell hits the 46006 buoy I relax…then wait about 12 hours to see it showing on the 46059 buoy…if the swell comes in pretty large and without a lot of wind being reported by the buoy (which would indicated the wave heights have increased because the storm is moving right over the buoy)…then I know we are in good shape.

7. I pack my surf gear and drive to my favorite NW swell spot (get there early before the swell arrives) and that way you can grab a couple before every guy and his cousin who saw it on the camera that morning get down to the beach.


Mike and Nancy said...


This is great. Can you give a link to the NOAA website where you got the image?

Adam Wright said...

Mike and Nancy,

Here you go...I will probably put this up in the text of the post as well.


lemur said...

Great information, Adam. Thanks for sharing how you use all this information. I'm learning quite a bit.


Dylan J. said...

So much useful information here!

Love this site and love learning the science behind forecasting