1 1 2 3 ON THE LANDFALL OF NORTHEASTERN PACIFIC TROPICAL CYCLONES JOHN, 4 LANE AND PAUL (2006) OVER NORTHWESTERN MEXICO 5 6 LUIS M. FARFÁN 7 Centro de Investigación Científica y de Educación Superior de Ensenada B.C. (CICESE) 8 La Paz, Baja California Sur, Mexico 9 10 ROSARIO ROMERO-CENTENO and G.B. RAGA 11 Centro de Ciencias de la Atmósfera 12 Universidad Nacional Autónoma de México 13 Mexico City, Mexico 14 15 16 Submitted to Monthly Weather Review 17 American Meteorological Society 18 16 July 2009 19 20 Corresponding author address: 21 Luis M. Farfán 22 CICESE, Unidad La Paz 23 Miraflores 334, La Paz, BCS 23050, México. 24 E-mail: [email protected] 1 2 25 ABSTRACT 26 27 This study is focused on the life cycle of Tropical Cyclones John, Lane, and Paul in the 28 Northeastern Pacific Ocean. These systems developed during the relatively active season of 2006 29 and made landfall over the coast of Northwestern Mexico. Based on a regional network, heavy 30 rainfall was documented throughout the Baja California Peninsula and mainland Mexico. A 31 gridded analysis reveals storm motion related to large-scale circulations including an anticyclone 32 over the Gulf of Mexico and a middle-latitude system approaching the western United States. 33 Tropical Cyclone John resulted in a maximum of total rainfall in the range of 350–510 mm, 34 concentrated along the storm track that moved over the peninsular mountains. These accumulations 35 set new records of daily rates with respect to the available dataset from the base period 1970-2005. 36 Later in the season, Tropical Cyclones Lane and Paul made landfall over the mainland and brought 37 low to moderate rainfall accumulations over relatively large communities in the state of Sinaloa. 38 Lane moved close to the coast and was a category-three hurricane at landfall with impact over the 39 southern Gulf of California. In contrast, Paul followed a recurving track that moved around Isla 40 Socorro and arrived to land as a tropical depression. An analysis of the official forecasts issued one 41 to three days prior to landfall reveals some track errors for John and Lane, more likely due to 42 limitations in the temporal coverage of upper-air soundings available from the operational network 43 established in central and western Mexico. 2 3 44 1. Introduction 45 The west coast of North America routinely experiences landfall of Tropical Cyclones 46 (hereafter referred to as TCs) from the Northeastern Pacific Ocean, a basin located east of 140°W. 47 During recent decades, several studies have been focused in TCs that resulted in landfall over the 48 coastal areas of Mexico. For example, Serra (1971) applied track information from the period 49 1921-1969 to document that TCs moving across the coastline had maximum frequency from 50 August through October. Jáuregui (2003) found that between 1951 and 2000, 65 hurricanes1 (88 51 tropical storms) made landfall in Mexico’s west coast and that 60% (49%) of them occurred in the 52 Northwest region of the country. Some of these TCs continued moving northward and, eventually, 53 they had influence on the weather conditions over the southwestern United States (Smith 1986; 54 Garza 1999). 55 In the present study, Northwestern Mexico is defined as the region located north of 20ºN 56 and west of 104ºW. As shown in Fig 1, this region includes the mainland states of Nayarit, Sinaloa 57 and Sonora as well as the Baja California Peninsula. The topography includes mountain ranges that 58 are oriented in a southeast-northwest direction: the Baja California range and the Sierra Madre 59 Occidental. The latter is a wide range (200-300 km) located over the mainland with maximum 60 elevations over 2000 m, while the former is a narrow range (50-100 km) with maximum elevations 61 just above 1000 m. Elevations above 1500 m are located over the state of Baja California, north of 62 28°N. Northwestern Mexico has a coastal length of 6408 km (National Institute of Geography in 63 Mexico, INEGI, http://www.inegi.gob.mx/inegi/default.aspx), which represents 57% of the total in 64 the whole country including the Pacific Ocean, the Gulf of California, the Gulf of Mexico and the 1 In this paper the term hurricane refers to maximum sustain winds > 33 m s-1, tropical storm to winds from 17 to 33 m s-1 and tropical depression to winds < 17 m s-1. 3 4 65 Caribbean Sea coastlines. The state of Baja California Sur (BCS), south of 28°N, has coasts along 66 both the Pacific and the Gulf of California equivalent to 42% of the total length in the northwest. 67 In 2005, 9% of the nation’s population lived in Northwest Mexico and the largest 68 communities were located close to the coast, over relatively flat terrain and below 300 m above sea 69 level (Fig. 1, Table 1). Sinaloa is the most densely populated state (45 inhabitants km-2) while BCS 70 is the least populated state (7 inhabitants km-2) in the region. These facts suggest that, upon TC 71 landfall, major differences should be expected between the impact from storm tracks that go over 72 the peninsula from those moving across the mainland. 73 Historical records for the Northeastern Pacific Basin, issued by the U.S. National Hurricane 74 Center (NHC), reveal the development of more than 500 named TCs during the period 1970–2006. 75 As also shown in Fig. 1, there were 63 landfall hits over Northwestern Mexico where the majority 76 of them occurred along the coasts of BCS and Sinaloa with, roughly, equal number of strikes per 77 state. Figure 2 displays the TC tracks of a couple of groups that, during such 37-year period, were 78 identified to make a first landfall over either the peninsula or the mainland. The figure inserts show 79 the temporal frequency of TC incidence, determined by dividing each month into three periods of 80 10 or 11 days. 81 The upper panel of Fig. 2 shows 27 TC tracks that first moved over the BCS. The incident 82 systems approached the peninsula from the south and most of them occurred from late August 83 through early October (see insert in Fig. 2a). Twelve TCs moved over land through the Gulf of 84 California, east from 110°W and across the eastern peninsula. Fifteen systems made landfall 85 through the Pacific coast and seven of them crossed the gulf to, eventually, reach the mainland. 86 During the same period, 25 TCs tracked only over the mainland (Fig. 2b). This group developed 87 later in the season with the highest frequencies occurring during the last third of September (22%) 4 5 88 and all of October (61%). Note that prior to landfall, and by Isla Socorro, the mainland tracks 89 tended to acquire an eastward component of motion and the preferred landfall region is bounded by 90 21°N and 28°N. Twenty-one systems moved across the state of Sinaloa, two over Nayarit and 91 another two over southern Sonora. 92 Farfán (2004) examined general features of the large-scale environment associated with a 93 sample of six tracks that, during the period 1992-2002, made landfall over Baja California. By 94 using the NCEP-NCAR reanalysis, the author found that mean 500-mb height fields consist of an 95 anticyclone over the Gulf of Mexico and a wave trough traveling eastward across the western 96 United States. A similar analysis was performed here and the results indicate that during landfall in 97 the mainland, there is a southward shift of the wave trough and an eastward displacement of the 98 anticyclone’s center to be located just south of Florida. This configuration allows TC motion over 99 the Sierra Madre Occidental along with the advection of a cooler and drier environment from the 100 Pacific Ocean, off the peninsula, into northern Mexico. 101 Further analysis of the 1970-2006 period suggests that stronger TCs tend to make landfall 102 over the mainland or over the southeastern edge of the peninsula. This is likely due, in part, to the 103 warmer SSTs over the Gulf of California with respect to the cooler waters of the California Current 104 in the Pacific (e.g., Mosiño and García 1974; Amador et al. 2006). Information on strong systems 105 at landfall is shown in the lower-left inserts of Figs. 2a and 2b. Some of mainland strikes are 106 associated with major hurricanes (this is, category-three or higher) in the Saffir-Simpson scale. In 107 fact, four out of 11 incident systems were major hurricanes while moving across the mainland 108 coastline. In contrast, 11 hurricanes moved through the peninsula with four of them along the 109 Pacific coast as category-one hurricanes and the rest of them went across the southern gulf. Only 110 Kiko (1989) and Paul (1982) were in the lower edge of the category-three hurricanes at landfall. 5 6 111 During the 2006 season in the Northeastern Pacific, from 27 May until 20 November, 18 112 named TCs developed and ten of them reached hurricane strength (Pasch et al 2009). These 113 numbers are slightly above the long-term averages for the period 1970-2006: 16.4 tropical storms 114 and 9.6 becoming hurricanes (Arguez 2007). In 2006, two systems made landfall in Northwestern 115 Mexico as hurricanes and one as a tropical depression. John and Lane arrived as category-two and 116 category-three hurricanes, respectively, and both became the third strongest TCs at landfall over 117 Baja California and over the mainland.