Eastern Pacific Hurricane Watch
Tuesday, May 19, 2010 Well, here we are again journeying into another Eastern Pacific Hurricane Season. The National Hurricane Center defines Eastern Pacific Hurricane Season as May 15th to November 30. The Atlantic Hurricane Season is 16 days shorter, beginning June 1 and ending November 30.
Baja Hurricane Season is still several months ahead of us, as we are now enjoying some of the best summer weather the year has to offer. Tropical cyclones have threatened Baja as early as the last week of July, but the statistics ramp up quickly beginning the third week of August, peak the third week of September and fall off just as quickly the second week of October.
The Eastern Pacific usually has the first Tropical Cyclone form between May 22 and 25. As the northern hemisphere is just beginning to warm toward summer, the ITCZ is much further south than it will be in late August and early September when it reaches it's northward most migration. The tropical waves moving west along the ITCZ will stimulate cyclonic activity and with the presence of +26°C water and in the absence of Shear, the Eastern Pacific will have the first tropical cyclone of the season.
OK, so there are a lot of big technical words there, and if you new to our Hurricane Watch Reports and Baja's tropical weather, there are some new terms to learn.
Tropical Cyclone
A Tropical cyclone is a well defined wind movement around a center in a cyclonic activity that forms over water and begins to feed itself. A Tropical Depression is the first level of a tropical cyclone with winds to 38mph. In the Eastern Pacific the Tropical Depression phase is usually short lived, as storms develop quickly.
A tropical cyclone gets a name and becomes a Tropical Storm when winds are above 39mph.
Tropical Wave |
Here are three explanations we found:1) A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere. 2) A hurricane goes through many stages as it develops. It starts as a tropical wave, a westward-moving area of low air pressure. 3) A kink, or bend in the normally straight flow of surface air in the tropics which forms a low pressure trough, or pressure boundary, and showers and thunderstorms. Can develop into a tropical cyclone. |
A Tropical Cyclone becomes a Category 1 Hurricane when winds top 74mph. There are then 5 levels of hurricane force on the Saffir Simpson scale. A Major Hurricane is a Tropical Cyclone of Category 3 or greater with sustained winds of 111mph or greater.
A side note here, this year the Saffir Simpson Scale will no longer include correlations with Tidal Surge as in previous years. It was found that a significant number of other factors played on the tidal surge affects.
Baja has only had one landfall of a Major Hurricane in the last 60 years, and that was Hurricane Kiko in 1986. Kiko made landfall along the East Cape Region of Baja California Sur and moved inland south of La Paz. Few North Americans lived in the region at the time and even fewer were around during the summer when the storm hit.
A few Major Hurricanes do make it in our direction Lisa was a Category 3 as it moved up the center of the Sea in the late 70's and a broken dam caused the death of several thousand people. Last year Hurricane Rick appeared poised to strike a Major Hurricane blow to Baja Sur, but as a late season storm, it fizzled before reaching Baja. It COULD happen again and there has been significant building and increase in population since the last big storm hit. The affects of a Major Hurricane could be profound.
ITCZ
Inter-tropical Convergence Zone. The region where the northeasterly and southeasterly trade winds converge, forming an often continuous band of clouds or thunderstorms near the equator. The ITCZ is the pipeline along which the most disturbed portions of the west bound tropical waves travel. As the Northern Hemisphere warms, it will migrate northward. In August a hook can form in the ITCZ and begin to help loop this disturbed tropical weather in our direction. Tropical cyclones, because of their counter clockwise rotation, naturally want to roll off to the west, like a spinning bowling ball. But as the disturbed air of a Tropical Wave meets the very warm waters west of Acapulco, Baja gets its look at a tropical cyclone threat. Most of Baja's tropical cyclone landfalls form about 250 miles WNW of Acapulco
Tropical Wave
There are three more specific and scientific explanation in the shaded box above. It is probably easiest to think of them as a high energy exhale in a burst, off the deserts of western Africa. Tropical waves are one of the key ingredients of tropical cyclone formation.
26°C Thermo Cline
Another of the key ingredients in tropical cyclone formation is +26°C (79°F) ocean water. Water above 26°C supports the escape of energy from the ocean's surface sufficiently rapid enough to support cyclonic activity. In mid August the waters west of Acapulco can easily reach 32°C, and this is when our season begins. Storms usually spin apart rather quickly once crossing into waters cooler than 26°C. This was the end of Category 5 Hurricane Rick in 2009.
Shear
Tropical cyclones are actually very delicate instruments. Shear is the lateral movement of winds across each other. The center column of a tropical cyclone lifts the warm air and energy from the warm ocean surface high into the atmosphere where it cools, releases its energy in lightening and rain and falls back earthward. If Shear interrupts this delicate column of energy flow, particularly in the early stages of storm formation, the cyclonic action will fail.
Tropical Cyclones after reaching a specific intensity can be called Hurricanes from the International Dateline to Greenwich, England and Typhoons in the western Pacific and Indian Ocean.
As stated earlier, we are still three months for any significant threat to Baja California Sur. The graphic left shows the weekly average Sea Surface Temperature for the Eastern Pacific Hurricane Basin. The all important 26°C thermo cline can be seen far south of Baja, Intersecting the south coast of Mexico near Barra de Navidad. Areas north of that thermo cline have little to worry about from tropical cyclone threats.
Another factor that effects weather patterns world wide is the El Niño Effect or ENSO (El Niño-Southern Oscillation) This year is an El Niño event and waters are currently 1.75°C to 2°C and not diminishing. Early season forecasts called for the El Niño to dissipate and possibly even provide a La Niño event by early winter 2011. Other forecasters now call for the El Niño event to possibly even increase, into what would be called a 
Strong Event, in excess of 2°C above normal. This year's ENSO is also occurring further west than usual. Last year the event provided Mexico with its driest season on record and landfall of only one tropical cyclone in Mexico. Unfortunately, that was Hurricane Javier which made landfall on the Pacific coast of central Baja.
This year was also unique in that the ENSO event formed further west than usual. It has been dubbed “El Niño Modoki” from the Japanese word meaning “the same, but different”. This has provided some unexpected results along the west coast of California this year. This is a new observation of the El Niño and what it may mean for the Eastern Pacific Hurricane Season is unclear.
In the strategic look at the current conditions of the Eastern Pacific Sea Surface Temperatures with the Anomaly graphic right, we see most the the basin is very near normal temperatures, even slightly below normal. Light green is normal areas, blue is colder than normal and yellow is slightly warmer than normal. Most of the basin is within 1°C of normal. What this means is there is a 'normal' amount of energy contained within the surface of the ocean to develop and feed a tropical cyclone.
We will build the two SST Analysis and Anomaly graphics as the weeks of the Hurricane Season pass, so you can see how and why SST's effect storm formation and paths.
Below is the wide angle surface chart for Tuesday, May 19, 2010. We don't see any developing Low's yet, but with a parade of tropical waves 2-3 days apart, stretching all the way back to the deserts of Africa, i would expect that one of them will generate a tropical cyclone in our region in the near future.
And now the fun part...
Last year I ran a respectable B+ on my Hurricane Watch Predictions. I'm not a meteorologist, but I have digested mountains of Baja Hurricane Data. I choose to predict the probability of a storm formation in a given week and an approximate threat zone ahead of the storm. For the next couple of months those storms that do form usually move harmlessly off into the Pacific. Since all indications are this is a 'normal year' in SST's there is no reason to suspect an early formation. Last year the same or slightly lessor degree of El Niño put off the first storm formation until June 18th. It also proved to be the driest year in Mexican recorded weather history. So I'm going to call for a quiet May in the Eastern Pacific.
Our Hurricane Watch Reports will be issued every two weeks until mid August, when our Tropical Cyclone threat begins to heat up. So look for this report again in the first week of June. Until then, fair winds....
Tomas Zyber
Our Eastern Pacific Hurricane Watch is an editorial/entertainment 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. or visit the Mexican Nation Metrological website for more information.
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