Wednesday April 26 2017

Posted by Tomas on May 14, 2013
  • How Hurricanes Form
    How Hurricanes Form
  • Current Sea Surface Temperature Analysis Graphic
    Current Sea Surface Temperature Analysis Graphic
  • Current Sea Surface Temperature Anomaly Graphic
    Current Sea Surface Temperature Anomaly Graphic
  • Color enhanced satellite image of Cat 3 Hurricane Odile hours before making landfall
    Color enhanced satellite image of Cat 3 Hurricane Odile hours before making landfall
  • Hurricane Odile's original projected path shown over the Sea Surface Temperature graphic. Odile passed more than 85 miles further east, directly over southern Baja.
    Hurricane Odile's original projected path shown over the Sea Surface Temperature graphic. Odile passed more than 85 miles further east, directly over southern Baja.

Over the past 13 years, I have authored more than 150 researched articles for the Eastern Pacific Hurricane Watch Report. This article is a compilation of the interesting tidbits I have gathered, the 'Best of..." if you will. This information has embellished my understanding of our late summer weather and I hope it will increase your knowledge and understanding of these tropical storms as well.

What is a Tropical Cyclone?

Tropical Cyclone is a warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this, they differ from extra tropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects). A tropical cyclone is that of Tropical Depression status or greater. (See Saffir-Simpson Scale below)

Also, see How Hurricanes are Named

What is the Monsoonal Trough or ITCZ?

Surface Charts now refer to this effect as the Monsoonal trough, formerly known as the Inter-Tropical Convergence Zone; a zonal band of low atmospheric pressure and thunderstorms caused by converging Trade Winds, rising air and intense thermal heating at or near the Equator; the location of the ITCZ shifts throughout the year resulting in wet and dry seasons in countries located in the tropics. The ITCZ acts as a pipeline for the tropical waves generated in Africa on their westward journey to the Eastern Pacific.

What is a Tropical Wave?

No, it is not alternately sitting and standing people at the Sun Splash Festival in Jamaica. Tropical waves are supercharged waves of air coming off the deserts of Africa. These waves travel along the Inter-Tropical Convergence Zone or 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 were a plethora of storms in the Atlantic/Caribbean side the Pacific was relatively tranquil

What are SST's?

Sea Surface Temperatures or SSTs are another factors to look at when we look at the chance of tropical cyclone formation. First, let's look at the SST Analysis. Tropical Cyclones need water warmer than 26°C to form and strengthen. Storms dissipate fairly rapidly once crossing the 26°C thermocline, indicated by the red line. Areas north of that line have little chance of being struck by a tropical cyclone. 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. The earliest hurricane to make landfall in Baja is August 15th and the latest is October 17th.

Does it matter if the ocean is warmer or colder than normal?

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. 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 °C. 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.

Does the warm water of the Sea of Cortez attract hurricanes?

Absolutely, in a previous article Publisher James Glover took a look at the effects of the Sea. Without a doubt, "The Sea of Cortez Sucks". How it steers the hurricane in its direction is still not entirely understood, but the fast evaporating water over warmer sea surface temps may weight the hurricane to that side. With the additional weight, the storms spin like a wobbly top, leaning toward the warmer water direction.

Do wind and humidity play a role in tropical cyclone formation?

Anyone who has ever lived through a hurricane season in Baja knows how warm and sticky that time of year can be. As the humidity increases, it acts as both an insulation and a battery for the energy of the sun. The moist air can retain much more of the sun's daytime energy through the night than would dry air. This prevents radiational cooling at night and increased evaporation, adding to the cycle. Winds diminish as the dramatic temperature differences between the Pacific, land and The Sea equalize. The cooling breezes stop at night and the air becomes very wet and still. Tropical cyclones draw on this stored energy, just like the most significant contributor, the ocean. The still air allows the circulation column of air to develop and the conditions become ripe for the formation of cyclonic action. Strangely enough, tropical cyclones are "ego-centric" and don't like the wind, other than their own.

How does the Pacific High play into the Baja Hurricane Season?

In the spring, the Pacific High is just several hundred miles west of Baja. The clockwise rotation or anti-cyclone spins wind from the WNW to NNW for Baja. From late winter to mid summer a ridge extends SE from the High toward the Socorro Islands. In a matter of speaking this acts as a 'fence' to deflect tropical cyclones to the west. As the summer progresses the High moves NW and the effects of the ridge on our region weakens. Normal barometric readings in the tropical areas can run around 1010Mb Storm tracks move north with the retreating High until in August Baja becomes vulnerable.

How are forecast tracks predicted?

My research comes from several sources for this, as with all hurricane articles. The NHC website and the British Meteorological Society provide some excellent information. I use  several books as well, many of these articles facts come from "The Devil's Music" by Pete Davies. The National Hurricane Center in Miami Florida is the major source for Hurricane prediction in this hemisphere. Although other countries have independent weather services, the satellite and computer resources available through the NHC provide much of the world's western hemisphere cyclone information. The NHC has 13 different computer modeling programs that function on three different premises. The first is the oldest, statistical analysis. The forecast predicts the path of the storm based on previous storm behavior. Much like rolling a ball bearing across a piece of glass with tracks cut into it. These systems are more primitive, but with an increasing database of detailed hurricane information, these models too have evolved to become more accurate. The second and more advanced technique are one that looks at a broad scope of weather systems and calculates their influences on each other, the 'if a butterfly flaps his wings" theory, applied to weather technology. With the amount of data now available it must be crunched on the NHC Cray Supercomputer. The third type of weather software is a hybrid of the two. This is truly monster software and this theory is the foundation of the NHC's most trusted model, the GDFL. As author Pete Davies put it, "If you want to sell a modeling software to the NHC it has to stack up favorably against the GDFL model."

Do individual software models provide accurate track projections?

As good as the GDFL model is, anyone with any knowledge of hurricanes will say emphatically "NO". Professionals consider putting significant weight on the prediction of any one model as "foolish" . The NHC and other forecasting services 'blend' the forecast tracks of all the computer models, weighting them accordingly to their performance in a particular situation. Sometimes they even tweak the storm path manually, to incorporate personal judgment. The result is the familiar teal ocean forecast model put forth by the NHC. Although storm tracks evolve over the development of a system the path models have proven incredibly accurate, very early in the storms development over the last 5 years. Model predictions for storm intensity, however, have lately proven to have somewhat of a lesser batting average with the model tending to over-predict storm development.

 

The Saffir-Simpson scale

Type Category Pressure (mb) Winds
(knots)
Winds
(mph)
Surge (ft)

Depression

TD

-----

< 34

< 39

 

Tropical Storm

TS

-----

34-63

39-73

 

Hurricane

1

> 980

64-82

74-95

4-5

Hurricane

2

965-980

83-95

96-110

6-8

Hurricane

3

945-965

96-113

111-130

9-12

Hurricane

4

920-945

114-135

131-155

13-18

Hurricane

5

< 920

>135

>155

>18

How are Hurricanes rated?

The Saffir-Simpson scale is what forecasters use to rate the intensity of a tropical cyclone. A Tropical Depression is the first tier of the tropical cyclone scale. Each level is double the intensity of the previous one. The Baja peninsula has been very lucky over the years to have only had the landfall of one Major Hurricane, Category 3 Hurricane Kiko in 1989. A Major Hurricane is one of Category 3 or greater. These storms are an entirely different game than that which Baja Hurricane Survivors are used to. Should Baja ever be forecast to take a Major Hurricane, treat it with a whole new level of storm respect.

Why doesn't Baja get the Monster Hurricanes like Katrina?

Until 2014 only two other Major Hurricanes, one of Category 3 or greater, had ever made landfall in Baja. Hurricane Kiko in 1989 came ashore on the then underpopulated East Cape region, but in 2014 Category 3 Odile came ashore in Cabo San Lucas and in an unusual development, became a Category 4 over land west of La Paz. The cause of this rare Major Hurricane Strike was warmer than normal ocean temps south of Cabo San Lucas combine with a neutral El Nino year, the most likely for landfalls of tropical cyclones in Baja.

Storm researchers have recently discovered it is deep warm water that generates the Major Hurricanes (ones Category 3 or greater. The Eastern Pacific has some very warm (+30°C/+86°F) water but it doesn't run very deep due to both currents and topography. Additionally, it takes time for a storm to 'wind up' and the Eastern Pacific Hurricane Basin is about the smallest of those worlds hurricane formation zones. The western Pacific has about 1800 miles of +29°C water that are very deep. Places like Guam often see storms of Category 4 and 5 and holds the record for some of the strongest storms. Most of the Major Hurricanes form in late August and travel west north of the ITCZ well south of Baja. (also see Baja Hurricane History)

What are Baja Tropical Cyclones like?

I have now weathered the eye of 4 Category 2 Hurricanes, several near misses and a couple of tropical storm hits. Baja tropical cyclones are usually smaller than those in the Atlantic. The first level of winds (the max force of the particular storm) extends out 25-35 miles . The next tier may extend out another 20-25 mile and so on. For example Category, 2 Hurricane Norbert passed about 90 miles north of La Paz, where we had a windy unpleasant day, with some rain. For those of you who have summered in the Mid-West, the occasional strong thunderstorm can present condition very similar to that of a strong Tropical Storm, even Category 1 Hurricane intensity. If you are not out in a boat or own a home built in an arroyo, our tropical cyclones usually just provide an awesome display of nature's power. (also see Baja Hurricane History)

What is the leading cause of death in Baja hurricanes?

In almost one word, "stupidity". Well, drowning is the leading cause of death in hurricanes worldwide and also usually the case here too. More often than not it is folks that fail to evacuate their home in time or attempt to drive across a flooded video and get swept away. I saw a large bus cross a flooded arroyo once. They removed the baggage, opened all the compartment doors so the water flowed through the bus and crossed. Even still this heavy vehicle was moved sideways on the road by the force of the water as it crossed. I waited for the water to receded. The buildings, particularly hotels in the tourist areas can easily withstand our normal storms. Things flood, trees get downed and the streets can be a mess, but Baja is use to this annual occurrence cleanup takes a matter of days. Buildings withstand the weather and over the last 5 years the major roadways have been refitted and bridged so that the days of closed highways is all but a thing of the past.

The best example of how 'hurricane savvy' the folks here in Baja are is last year a pair of young girls was collecting canned food to send to Houston, following Category 2 Hurricane Ike. They were baffled by the cities inability to cope with a simple Cat 2 storm, something La Paz recovers from in a matter of hours. The trick here is no stick homes build on beachfront sandbars. (well, except for the La Paz Magote project)

What is a normal year for Baja Tropical Cyclones

2009 was a slightly above normal year for the number of named storms. although an abnormally large number remained tropical storms, we were short a few hurricanes. However, 2009 also generated a greater than a normal number of Major Hurricanes, two of which threatened Baja. Baja felt the impact of the first as a Category 2 Hurricane (Jimena) and Rick dried up just short of our peninsula.

A normal year provides about 15 Named Storms (Tropical Storm intensity or greater) About 9 of those storms are of Hurricane intensity and 4 of them are Major Hurricanes (Category 3 or greater) Interestingly enough the period from 1997 to 2008 was less active than the period of 1966 to 1996 with fewer named storms, fewer hurricanes, and fewer major hurricanes. Part of this may be due to better analysis tools. On an average over the last 12 years, Baja has received an average of just about 1 tropical cyclone landfall per year more than 1/2 of them were hurricanes. In four of the past twelve years, Baja has received a double whammy of two tropical cyclones making landfall. Additionally, about every other year, Baja has a storm pass close enough to bring heavy weather, without making landfall, a near miss if you will. (also see Baja Hurricane History)

As you can see by the graphic right, it is a pretty steady progression of named storms from early July through late September. Hurricanes come at a steady pace after mid-July and Major Hurricanes come at a regular pace from early august to early October.

This information alone makes you a better-informed hurricane tracker. Thanks for making the BajaInsider one of the leading sources for information on Baja Tropical Cyclones.

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