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TROPICAL CYCLONES AFFECTING LA PAZ/PICHILINGUE

Specific tropical cyclone data, containing storm tracks, wind and pressure data, etc., are available starting in 1949. However, prior to 1966 satellites were not used operationally and there are likely some storms that tracked well offshore from La Paz/Pichilingue and the Baja Peninisula and are missing from the data set. Records of storms off the west coast of Mexico (the Eastern North Pacific Basin) are shorter than they are for other basins and, before 1949, the records are so fragmented that they are of little use in climatological analysis. The reason for this is that most of the storms in the Eastern Pacific do not affect land and zonal shipping routes. After the beginning of the operational satellite era in 1966, many more storms than previously thought were noted between Mexico and the Hawaiian Islands.

The climatology of tropical cyclones for La Paz and Pichilingue are combined here since the two harbors are less than 11 nmi apart. Table IV-1 contains a descriptive history of all the recorded 86 tropical cyclones and hurricanes passing within 180 nmi of La Paz/Pichilingue during the 53-year period 1949-2001. Unless otherwise indicated, all of the tropical cyclone statistics utilized in this report for storms passing within 180 nmi of La Paz/Pichilingue are based on the data set used to compile Table IV-1.

The majority of tropical cyclones originate in the area to the south-southeast of La Paz/Pichilingue and 48 % of the tropical cyclones originated within 72 hours of the Ports (Figure IV-22). Note that the dark circles indicating the 72-hour locations are generally southeast of La Paz and that the tropical cyclones normally follow the coastline in a northwesterly direction. Accordingly, ships transiting from the Port need to be aware of the rapid development of tropical cyclones as they proceed through the Gulf of California to the open ocean through what the pilots refer to as "hurricane alley."

Although these tropical cyclones can generate winds in excess of 100 kt, they historically have not produced large wind waves and huge tidal surges in La Paz/Pichilingue that do so much damage elsewhere. The Ports of La Paz and Pichilingue are in protected bays and are normally protected from high seas because of the surrounding topography. The average speed of advance for tropical cyclones at the latitude of La Paz/Pichilingue is about 11 kt.

Although the tropical cyclone season for Mexico is considered to extend from June through October, Table IV-2 shows that La Paz/Pichilingue's season extends from June through November. However, only two storms were recorded for each of the two months of June and November throughout the 53-year period 1949-2001. September had the greatest tropical cyclone activity, with 34 of 86 storms (39.5 %) occurring during that month. Of the 86 storms in the data set, 37 were of hurricane strength (greater than or equal to 64 kt) within 180 nmi of La Paz. Table IV-2 also shows the average direction towards which storms were moving when they were at CPA to La Paz/Pichilingue. The average movement for all storms is 347° at 11 kt. The average speed by month is very constant and ranges from 11-13 kt. 

Figure IV-23 shows in seven-day increments the annual distribution of the 86 tropical cyclones that entered the 180 nmi threat radius around La Paz/Pichilingue. The period of maximum activity, from June 11th through November 21st, is clearly shown. It is also interesting to note the increased activity during September and the first week of October.

Figure IV-24 depicts the chronology of the 86 tropical cyclones that passed within 180 nmi of La Paz during the 53-year period 1949-2001. As shown in the figure, there is an average occurrence rate of 1.62 storms per year for all tropical cyclones, regardless of intensity. The recurrence interval of all tropical cyclones is 0.6 years. There have only been eleven years since 1949 when no tropical cyclone entered La Paz's 180 nmi threat radius. 1953, 1956, 1961, 1972, 1975, 1980, 1983, 1988, 1991, 1992 and 1996 had no storms passing within 180 nmi of La Paz/Pichilingue.

Figure IV-25 shows the octants from which the 86 tropical cyclones were moving when they were at CPA to La Paz/Pichilingue. As shown in the figure, the predominant threat directions are from the southeast and south octants. A total of 32 storms (37.2 %) approached from the southeast and a total of 28 (32.6 %) approached from the south. It must be remembered that the figure represents tropical cyclone movement at CPA, and may not represent the tropical cyclone's initial movement towards La Paz/Pichilingue. Note that both the threat direction and the slow speed of movement are important considerations for evasion at sea or making storm preparations in port.

Figure IV-26, Figure IV-27 and Figure IV-28 show the tracks of the 86 tropical cyclones separated into three periods. As shown in all three figures, the movement of the 86 tropical cyclones that entered La Paz/Pichilingue's 180 nmi radius can be described as fairly consistent. It is important to note that 48 % of all storms developed within 72 hours from the closest point of approach to La Paz/Pichilingue. During the June 1-August 31 period, 1949-2001, the tropical cyclone tracks branch out north of La Paz/Pichilingue with the majority of the tropical cyclones passing west of the Port. During the September 1- 30 period, the majority of storms track parallel to the west coast of Mexico and branch out after passing north of La Paz/Pichilingue. During the October 1-November 30 period, the majority of storms recurve to the east and most pass east of the Port.

Figure IV-29, Figure IV-30, and Figure IV-31 are the statistical summaries of threat probability based on tropical cyclone tracks for the period 1949-2001. The summaries are separated into three periods to coincide with the tracks presented in Figure IV-26, Figure IV-27 and Figure IV-28. The data is presented with solid thin lines representing "percent threat" for the 180 nmi radius circle surrounding La Paz/Pichilingue. The solid thick lines represent approximate approach times to La Paz/Pichilingue based on the climatological speeds of movement.

In Figure IV-29 for example, a tropical cyclone located near 19°N 106°W has approximately a 40 % probability of passing within 180 nmi of La Paz/Pichilingue during the June 1 to August 31 period. In addition, this tropical cyclone would reach La Paz/Pichilingue in 11/2-2 days if the speed remains close to the climatological normal for tropical cyclones passing within 180 nmi of La Paz/Pichilingue.

Wind

Wind measuring instruments are located in the Captain of the Port (COTP) office 0.2 nmi from the Dock in La Paz and at the National Water Commission Building 2 nmi from the Port. The measured winds at the COTP office are considered to be representative of those experienced by ships in the Port of La Paz. Winds are probably stronger over the water than indicated by instrumentation at either the National Water Commission or at the La Paz Airport. No wind measuring instruments are located in the Port of Pichilingue. 

Current meteorological conditions every 30 minutes with additional webcam photos in the vicinity of the Bay of La Paz can be obtained through the following San Diego State University CIBNOR/Comitan website: http://www.cibnor.mx/meteo/icibmet.html. Wind speed and direction are included in the tabular portion. 

A notable weather phenomenon that occurs occasionally during the summer hurricane season is a "Torito". These strong southerly squalls can exist and reach 45-50 kt sustained winds for ½ to 1 hour in duration. Toritos occur during the months of July and August. Indicators of this event are thunderstorms approaching from the south. 

Prevailing winds are from the south in the summer (April to October) and from the north in the winter (November to March).

Waves

Ships tied up at the Dock in La Paz and the Commercial Pier in Pichilingue are not impacted by open ocean waves since they are in protected bays. According to the Pilots during the site visit in February 2002, the maximum wave height experienced inside the Ports has been 1.6 ft (0.5 m) and outside the Ports has been 8.2 ft (2.5 m).

Storm Surge

Dr. Eleonoro Romero Vadillo of the Autonomous University of Baja California Sur did a study on storm surge in the area and indicated that Hurricane Liza (October 1976) had caused a 6.6 ft (2 m) storm surge in the Port of La Paz and a 3.3 ft (1 m) storm surge in the Port of Pichilingue. Additionally, Hurricane Juliette caused a 4.9 ft (1.5 m) storm surge in La Paz. Pilots indicated during the site visit in February 2002 that storm surge had not had a significant impact on ships in Pichilingue during recent tropical storms.

Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/mexico/lapazpic/text/sect7.htm