Tropical cyclone landfall probabilities and track analysis for the Eastern North Pacific: 1970-2009

This work is focused on the study of tropical cyclones (TCs) that made landfall over the Mexican Pacific coasts during the 40-year period from 1970 to 2009. The study includes statistical aspects for different space-time scales, like intraseasonal, annual, and monthly frequencies; preferred landfalling regions, category distribution, and genesis location, considering those TCs originated in the Eastern North Pacific (ENP) basin east of 125ºW . In the analyzed period, a total of 583 TCs occurred in that region, accounting for an average of 14.6 TCs/year, with a standard deviation of 3.5; the percentage of occurrence of minor hurricanes (categories 1 and 2) was 30.6% and of major hurricanes (categories 3 to 5) was 26.2%. Of a total of 331 TCs reaching hurricane intensity, 54% attained minor category and 46% were classified as major hurricanes. A total of 98 TCs struck directly over the Mexican Pacific coasts, that accounts for an annual average of 2.4 with a standard deviation of 1.6, and represents around 17% of the total activity in the ENP. The annual percentage of landfalling TCs reaching tropical storm (TS) strength was 29.6%, that of minor hurricanes was 40.8%, and of major hurricanes was 29.5%. There is an insignificant correlation (r=0.11) between the number of landing TCs and the total number of TCs per year; the correlations are too low even if subseasons are considered. Along the TC season, the number of landings peaks in September and October (36% and 30%, respectively), followed by June (14%). However, their category distributions are quite different since TS and minor hurricanes account for 71.4% in September and 44.8% in October, while major hurricanes account for 28.6% in September and 55.2% in October; actually, the only two maximum strength category 5 hurricanes reaching the coasts occurred in October. The frequency distribution of landing dates by thirds of a month shows that the last third of September and the first third of October are the more active periods, accounting for more than 32%. Noticeable are the low occurrences during the month of July and the first two thirds of August, showing zero landfalls in the first third of August during the analyzed period.

The Mexican states with more TC hits are Baja California Sur (31.6%) and Sinaloa (23.5%). Even though the state of Sonora has just one direct TC hit, it is important to mention that a considerable number of TCs crosses the Baja California Peninsula reaching the coasts of Sonora and Sinaloa. The spatial distribution of landings has a notable variability along the season, being more frequent over the central-southeastern states during May-July while during August-October most of the landings occurred over the central-northwestern states. Large interannual variability in the number of landings is observed, and also at 5-year periods the variability can reach 100%. There is not a clear tendency or preference for the occurrence of TCs in any particular ENSO period or event. However, hurricanes with categories 4 and 5 were observed only during El Niño or neutral conditions. Probability distribution shows that the most probable case is the occurrence of two landings (~0.26) in an average year over the Mexican Pacific coasts, while zero landings has a chance of ~0.1 and six landings of ~0.05. Landfall probabilities for some Mexican states and a monthly analysis of the TC track types are also shown.