Eastern Pacific Hurricane Watch - Starting the Season with a Bang!

SST Analysis

Tropical cyclones thrive in waters warmer than 26° C and degenerate in waters below that temp. Areas south and east of the red line have the potential for a tropical storm strike

Last year was a tough year for meteorologists in the Atlantic. Based on data through January of 2006 they forecast an Atlantic Hurricane Season nearly twice as intense as normal. Instead,  a far lighter than normal season occurred giving forecasters the black eye of a 67% error. Some of those who believe that global warming is a fairy tale were quick to seize on this error to discredit science. There were a number of factors that materialized following the January data that were responsible for the error in forecasting. The current degree of sophistication in weather forecasting is a very new science and forecast models are built on historical data. This historical data reaches back maybe 100 years in the Pacific Basin. The accuracy of this data has improved exponentially over the last 40 years. Early satellite tracking of storm paths began in the late 1960's, satellite radar, infrared and Doppler radars have only become an effective tool in the last 25 years and wind speed satellite imagery has been around less than a decade. As you can see, the data sample is probably less than 200 hurricanes worth of detailed Pacific (specific) data.

Despite this the Eastern Pacific long range forecast has held to a much better batting average than it's Atlantic counterpart. The Pacific forecast holds to about a 89% accuracy rating compared to the Atlantic's 78%. This is good news for us here in Baa Sur, as they are predicting a lighter than average hurricane season for 2007

SST Anomaly

The colors represent deviation of this years water temperatures from the norm. Green is normal, blue colder than normal and yellow warmer than normal waters.

We have two active tropical cyclones at the time of the writing of this article, TD Alvin, expected to wither away harmlessly in the Pacific and TS Barbara which may pose a Hurricane 1 threat to southern Mexico this weekend. Neither of these storms were spawn by tropical waves. looking at the wide angle Surface chart below we can see there is our first tropical wave of the season in the pipeline.

Tropical waves are supercharged waves of air coming off the deserts of Africa. These waves travel along the Inter Tropical Convergence Zone or ITCZ across the Atlantic and the Pan-American Isthmus to the Pacific. Those waves that don't spawn storms in the Atlantic stand a pretty fair chance of stimulating a cyclone in the Pacific. This is why in July of 2005, when there was a plethora of storms in the Atlantic/Caribbean side the Pacific was relatively tranquil.

Sea Surface Temperatures are another factor to look at when we look at the chance of tropical cyclone formation. First let's look at the SST Analysis above. Tropical Cyclones need water warmer than 26°C to form and strengthen. Storms dissipate fairly rapidly once crossing the 26°C thermo cline, indicated by the red line. Areas north of that line have little chance of being struck by a tropical cyclone. In the animation, you can see how the red line has begun to advance northward as the ocean warms. Also note the growing area of +30°C water in what we will call the Eastern Pacific Hurricane Birthing Zone. Almost all of our Eastern Pacific hurricanes form in this region. It will be early August before the 26°C thermo cline advances far enough north to include Baja. The earliest tropical cyclone to make landfall in Baja is August 15th and the latest is October 17th.

Sea Surface Temperature Anomalies are a second tool to look at when anticipating hurricane formation. SST measures the amount of kinetic energy in the surface of the ocean. The more energy, the greater the likelihood of cyclonic formation. When we look at the anomaly, or difference over normal years, water above normal presents a greater than average threat of storm formation. On this animation we can see the La Nina event occurring at the bottom of the frame, near the equator. The dark blue represents colder than seasonal water. Light blue water represents normal temperatures while yellow and eventually red, represents warmer than normal water. The scale in in °C. Of slight concern to us early in the season in the above normal temperatures in the hurricane birthing zone off the southern coast of Mexico. The entire region is up to a little more than 1°C warmer than normal. This is only significant when you think about how much energy it takes to make a region that large, warmer than normal. With Barbara active in that region we can expect that next week some of that energy will be dissipated.

So now the fun part... what is in store for the week ahead? I think Alvin is a done deal, headed out harmlessly into the Pacific to fall apart. On the other hand, the jury is still out on TS Barbara. The NHC models have consistently overestimated the durability of tropical cyclones over the last year. I think Barbara may strengthen some, but never reach the peak intensities the forecasts currently call for. Our first tropical wave has to travel across the jungles of northern South America before reaching the Pacific. It will need 4-6 days to reach the basin and in that time adequate moisture and energy may reform, following the passage of Barbara. I am going to bet that the tropical wave will fall on dry air if it even makes it to the Pacific and we'll probably have to wait a week or two for the next storm formation. Either way, we will be warm and dry here in Baja Sur.

Until June 12th... Clear skies and fair winds!   Tomas

Our Eastern Pacific Hurricane Watch is an editorial analysis of data from the National Hurricane Center, NASA and NOAA and is based on information provided by the same, but is an amateur endeavor. For actual storm information readers should refer to notices and warnings posted by the National Hurricane Center.