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Eastern Pacific Hurricane Watch
Tuesday, August 18, 2009 Hurricane Guillermo was spawned in the Eastern Pacific last week and reach Category 3 Hurricane Intensity as it moved into the Central Pacific Basin late in the week. It qualified as the second Major Hurricane along with Felicia which reached Category 4, but outside our Eastern Pacific Basin.
This keeps us right on track with a normal year, which delivers about 7 named systems by mid August. And we are slightly ahead of the curve now on Major Hurricanes with 2. This almost needs an asterisk by it as one of the storms, although originating in the Eastern Pacific, did not become a Major Hurricane until it was in the Central Pacific basin.
August 15 begins the real Hurricane Season in Baja. The earliest hurricane to make landfall in Baja did so on the 15th of August. The next few weeks will continue to see a stream of tropical systems develop and we will need to begin to pay attention to those that come from our Hurricane Birthing Region off the coast of mainland Mexico, between Puerto Vallarta and Acapulco.
One sure sign that our hurricane season is on the way is the increased humidity and afternoon thunderstorm activity.
To our good fortune, the Atlantic Basin is finally beginning to absorb some of the tropical waves from Africa and generate a few tropical cyclones of their own. This week they took a great stride toward catching up in what has been a very quiet season in the Atlantic with 3 tropical cyclone formations. This is to our good fortune because the energy contain in these tropical waves moving west from the deserts of Africa is used up and disperse to greater and lesser extents by storm formation in the Atlantic. When the Atlantic is busy, we usually get a break from cyclone formation.
The Sea Surface Temperatures (or SST's) of the waters surrounding Baja continue to warm up and nearly the maximum amount of Pacific coast is now within the 26°C thermo cline (indicated in red) and is susceptible to hurricane strength landfall. Tropical cyclones need waters warmer than 26°C to support the cyclonic action. (along with many other factors) The 26°C thermo cline will continue to edge northward over the next few weeks, but Mag Bay is usually the most northern progression. Now, tropical cyclones can exist over cooler waters, for example last years Hurricane Norbert, but will dissipate rapidly when so.
This week we see an increase in the area of +29°C waters off the southern coast of Mexico while the +30°C waters actually contracted. This was extensively due to winds through the Tehuantepec.
As we look at the Sea Surface Temperature Anomaly graphic left is the amount of water very near the peninsula is now just slightly above normal. The area of water slightly warmer than normal has significantly diminished off the southern coast of the mainland, while the waters SW of Cabo San Lucas still remain slightly warmer. This is good news, because the waters over much of the area where the Baja Hurricanes come from is at or near normal for this time of year. This translates into the amount of kinetic energy stored in the ocean than is available to spawn tropical cyclones is near normal.
Taking a look at the wide angle surface chart below from Tuesday August 18, 2009 we see what is in the pipeline for us and how the Atlantic hurricanes affect our st rom development. Below we can see four tropical waves (orange arrows) moving west along the ITCZ from Africa. The west most wave is already too far west to be of concern to Baja and the second will find little moisture to spawn a tropical system until it too is west of the threat window to Baja Sur. The third wave may be the one to watch, as more tropical moisture becomes available by late in the week. We should have 4-5 days of time off from the passage of tropical waves cause by the generation of Hurricane Bob in the Atlantic. The fourth wave is looking well into next week and the whole weather picture in the Eastern Pacific will change by then.
Hurricane Bob (red arrow) is forecast to become a Major Hurricane as it churns NW outside the leeward islands. AS of now the forecast calls for the storm to bank more the to the NNW and have little chance of landfall on the continental US. But it is still early and forecasts tracks can certain bend enough in 5 days that residents of the southern and central east coast will keep an eye on Bob.
More below...
Now the fun part, where I gaze into my crystal ball and prognosticate on the Cyclonic fortunes in the week ahead. My great record holds with the formation of Hurricane Guillermo late last week. Again this week I am going to quote the Ouija Board as saying late in the week we will have another tropical cyclone formation , well west of the threat window to Baja from the third tropical wave. The remainder of the forecast period should not see the passage of a tropical wave. My bet is Baja is safe again for the week ahead, but don't take my word for it.