Eastern Pacific Hurricane Watch -  A Very Quiet June

So, "wazzup" with June? By the first week of July the Eastern Pacific has usually had 4 named systems. This year, just two. We certainly have had our share of Tropical Waves march through the basin. But Tropical waves are just one of the ingredients in tropical cyclone formation. Fewer than 1 in 10 tropical waves ever generate a tropical cyclone.¹

The Tropical Wave is just the trough of superheated air driven west from the Sahara Desert almost half the planet away along the Inter Tropical Convergence Zone or ITCZ. The wave then needs to find some hot water, water in excess of 26°C (79°F). The hot dry air sucks the water vapor from the surface of the ocean and upward into the atmosphere, where it becomes cooler and condenses out on dust particles driven from the desert sands, it begins to rain and an engine has been created.

Now, things need to be just right at this point to allow the fragile mechanics of a tropical cyclone to get started. The system needs still air, free from conflicting multilevel currents, vertical shears and cross winds. This allows the column of this convection to become established. Water vapor rises, cools at high altitudes and precipitates out of the air, becoming rising water vapor again as it reaches the hot dry surface air. A nearby dry air mass or winds from opposing systems can preclude development. This adjacent dry air mass is why June has been so quiet. The lack of significant moisture and increased mid level winds, possibly attributed to the mild La Nina effect, have kept our June tropical waves from becoming tropical cyclones.

I've been doing some reading on the subject of hurricanes, as I always try and 'tune up' for the real threat to Baja later in the season. I learned that hurricanes need a specific location to form as well. The Coriolis Effect is what makes your toilet flush counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. it is also an integral factor in the formation of tropical cyclones.

Tropical Cyclones must form about 300 miles away from the equator for there to be enough of the earth's spinning effect to cause the storms to begin to rotate - counter clockwise in the northern hemisphere. Now, I have stood on the Equator and believe me, RIGHT ON the equator the water literally falls through a funnel in a disorganized fashion. No more than 15 meters north or south, the water spins in the appropriate direction. Tropical cyclones need a little more energy applied to them to start rotation, and therefore can not form closer than 300 miles from the equator

The effect is also responsible for the initial movement of the storm. As the storm spins the northern edge and southern edge of the storm can be hundreds of miles apart, north to south. This means that the Coriolis Effect has a much greater influence on the northern side of the storm than the southern. As the storm rotates the wind 'bunches up' at two locations, about 1 and 7 o'clock in the NNE and the SSW side of northern hemisphere storms. Imagine a group of about 20 people holding hands in a large circle. As the group turns as a whole circle on a flat surface, everything is orderly. Now, imagine that there is a hill on the south corner (where the effect is less and the rotation of the storm receives less push) and a slide on the north corner. (where the effect is trying to make the storm spin faster). The ring of people won't remain organized for long, crowds bunching up at the climb and slide. Right after the slide, people will run to catch up with the person in front of them,

accelerating the ring. This is why the leading/right side of a northern hemisphere tropical cyclone packs the worst punch and why often times, as John showed us in 2006, that the worst rain comes when the storm bunches up on the SSW corner. This is also why the weather chart symbol for a tropical cyclone looks like it does!

Finally lets take a look at the water temperature in the Hurricane Birthing Zone. The all important 26°C thermo cline is edging closer to Baja Sur. Already 1/2 way from PV to Cabo and well up the mainland side into the Sea it will be another month before that line gets close enough for us to start to worry about landfall of a system. Tropical cyclones disintegrate quickly once over cooler waters and the worst we could expect until that time is a lot of rain and some wind. But the +30°C water is becoming a significant area on our map and it's only a matter of time before the ITCZ delivers a Tropical Wave to the area and we have a storm to watch.

Now it's time for the fun part... I dropped a few points in the last Hurricane Watch, as I called for TD3E to mature not only to a named storm but to a Cat 1 Hurricane. Well, TD3E just drifted away into oblivion. I was partly correct in predicting that a system would form this past week, it mature as of the writing of this article into a Tropical Low. (see color satellite image above) So, I'm only getting 25% for last week. I just can't imagine, the next two weeks will be as quiet. We have a fewer Tropical Waves headed at us in the next 7 day window, but that tropical water is getting awful hot and the thunderstorms are bound to start to kick up as the Pacific High drifts northward. There is this Tropical Low, but it is moving fast and will soon run out of hot water as it moves west. I see a TD at best for this system. There is one tropical wave just entering the basin, but the previous system has dried things out again. The sun will continue to beat down and the water get hotter in this clear air. However, late this weekend another wave will enter the basin, I'm going out on a limb to say it will generate a Tropical storm early next week that will head off into the Pacific late next week. The week following, my Ouiji Board tells me we will see our first Hurricane of 2007 in the Eastern Pacific! Baja may see some precipitation spin-off from a storm potential, some 10 days away, but the Pacific High is keeping the air too dry for that right now.

In two weeks we'll talk about Computer Prediction Models and how they fail along with Deep Water Convection and how it strengthen storms, rapidly... bet you just can't wait!

Until July 11th ... 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.

¹ Pete Davies, The Devil's Music – In the Eye of the Hurricane, London, Michael Joseph Press, 2000