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 Puerto Vallarta and are missing from the data set. Table II-1 contains a descriptive history of all the recorded 104 tropical cyclones and hurricanes passing within 180 nmi of Puerto Vallarta during the 51-year period 1949-1999. Unless otherwise indicated, all of the tropical cyclone statistics utilized in this report for storms passing within 180 nmi of Puerto Vallarta are based on the data set used to compile Table II-1.
The majority of tropical cyclones originate in the area to the southeast of Puerto Vallarta and south of Acapulco. These storms normally head northwest parallel to the coast or west out to sea. Storms that do approach Puerto Vallarta from the southeast are weakened by passage over the westward extension of the landmass. Although these tropical cyclones can generate winds in excess of 100 kt, they do not produce huge tidal surges in Puerto Vallarta that do so much damage elsewhere. Puerto Vallarta is normally protected from high winds and seas because of the surrounding topography. It is also interesting to note that 66 of the 104 tracks did not extend back 72 hours before reaching CPA to Puerto Vallarta. Accordingly, ships transiting from the Port need to be aware of the rapid development of tropical cyclones as they proceed through what the pilots refer to as "hurricane alley." The average speed of advance for tropical cyclones at the latitude of Puerto Vallarta is about 10 kt.
Although the tropical cyclone season for Mexico is considered to extend
from June through October, Table II-2 shows that Puerto
Vallarta's season extends from May through November. However, only two storms
were recorded during May and one storm was recorded during November throughout
the 51-year period 1949-1999. September and October had the greatest tropical
cyclone activity, with 57 of 104 storms (54.9%) occurring during those two
months. Of the 104 storms in the data set, 33 were of hurricane strength (
64 kt) at CPA to Puerto Vallarta. Table II-2 also shows
the average direction towards which storms were moving when they were at CPA
to Puerto Vallarta. The average movement for all storms is 337° at 10 kt.
The average speed by month is very consistent and ranges from 8-11 kt.
Figure II-4 shows in seven-day increments the annual distribution of the 104 tropical cyclones that entered the 180 nmi threat radius around Puerto Vallarta. The period of maximum activity, from May 21st through November 11th, is clearly shown. It is also interesting to note the bimodal distribution (June and September).
Figure II-5 depicts the chronology of the 104 tropical cyclones that passed within 180 nmi of Puerto Vallarta during the 51-year period 1949-1999. As shown in the figure, there is an average occurrence rate of 2.04 storms per year for all tropical cyclones, regardless of intensity. The recurrence interval of all tropical cyclones is 0.5 years. There have only been seven years since 1949 when no tropical cyclone entered Puerto Vallarta's 180 nmi threat radius, but in two of the 51 years, five tropical cyclones passed within 180 nmi of Puerto Vallarta!
Figure II-6 shows the octants from which the 104 tropical cyclones were moving when they were at CPA to Puerto Vallarta. As shown in the figure, the predominant threat direction is from the southeast. It must be remembered that the figure represents tropical cyclone movement at CPA, and may not represent the tropical cyclone's initial movement towards Puerto Vallarta. 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.
As shown in Figure II-7, the movement of the 104 tropical cyclones that entered Puerto Vallarta's 180 nmi radius can be described as fairly consistent. The dark circles in the figure indicate the locations of the 104 tropical cyclones when they were 72 hours from CPA to Puerto Vallarta. Note that the dark circles are generally southeast of Puerto Vallarta and the tropical cyclones generally follow the coastline in a northwesterly direction. However, 68 of the 104 tropical cyclones tracks did not extend back 72 hours before reaching CPA to Puerto Vallarta.
Many storms recurve to the north of Puerto Vallarta and those storms that do happen to make landfall near Puerto Vallarta are weakened by the topographic features. Although many storms pass within 180 nmi of the Port they mostly bypass to the west.
Figures II-8 and II-9 shows the tracks of the 104 tropical cyclones separated into two periods. During the May 1-September 15 period, 1949-1999, the tropical cyclone tracks branch out just south of Puerto Vallarta with the majority of the tropical cyclones passing west of the Port. During the September 16-November 30 period, many of the storms do recurve to the east, but normally north of Puerto Vallarta. Those closest to the Port are less than hurricane intensity and historically have not impacted the Port. According to the information received during the site visit in February 2000, none of the tropical cyclones caused damage to ships in Puerto Vallarta.
Figures II-10 and II-11 are the statistical summary of threat probability based on tropical cyclone tracks for the period 1949-1999. The data is presented with solid lines representing "percent threat" for the 180 nmi radius circle surrounding Puerto Vallarta. The heavy dashed lines represent approximate approach times to Puerto Vallarta based on the climatological speeds of movement. In Figure II-10 for example, a tropical cyclone located near 13°N 99°W has approximately a 20 % probability of passing within 180 nmi of Puerto Vallarta during the September 16 to November 30 period. In addition, this tropical cyclone would reach Puerto Vallarta in 3-4 days if the speed remains close to the climatological normal for tropical cyclones passing within 180 nmi of Puerto Vallarta.
Examining available wind data for selected recording stations in and around
Puerto Vallarta, 12 tropical cyclones were found to contribute
22 kt and 9 tropical cyclones contributed
34 kt in the 19 year period 1980-1998. However, no wind data is recorded in
the Harbor. The pilots assured us during our visit in February 2000 that they
were not aware of any situation in which winds or waves from tropical cyclones
had impacted ships at the piers or at anchor.
Ships steaming in the southern part of the Bay of Banderas or at the anchorages and piers in Puerto Vallarta are not normally affected by open-ocean wave motion. According to information received during the site visit in February 2000, waves up to 8 ft high caused by hurricanes have eroded beaches and damaged restaurants and hotels on the north side of the bay but did not affect the Harbor. As discussed previously, the landmass topographic features and the refraction of the waves minimizes the wave heights and lessens the effects on the anchorages and berths in Puerto Vallarta.
Storm surge has not affected the Port of Puerto Vallarta during any previous tropical storms.