1026 MONTHLY WEATHER REVIEW VOLUME 134 ANNUAL SUMMARY Eastern North Pacific Hurricane Season of 2004 LIXION A. AVILA,RICHARD J. PASCH,JOHN L. BEVEN II, JAMES L. FRANKLIN,MILES B. LAWRENCE, AND STACY R. STEWART Tropical Prediction Center, National Hurricane Center, NOAA/NWS, Miami, Florida (Manuscript received 5 April 2005, in final form 2 August 2005) ABSTRACT The 2004 eastern North Pacific hurricane season is reviewed. It was a below-average season in terms of number of systems and landfalls. There were 12 named tropical cyclones, of which 8 became hurricanes. None of the tropical storms or hurricanes made landfall, and there were no reports of deaths or damage. A description of each cyclone is provided, and track and intensity forecasts for the season are evaluated. 1. Overview waves in the eastern North Pacific has been docu- mented in numerous occasions, for example, Avila et Two notable aspects of the 2004 season in the eastern al. (2003). Most of the tropical cyclones in 2004 origi- North Pacific hurricane basin (from 140°W eastward nated from tropical waves that moved westward from and from the equator northward) were that none of the Africa across the Atlantic basin before entering the tropical storms or hurricanes made landfall and that eastern North Pacific. These waves became convec- there were no reports of deaths or damage attributed to tively active and spawned tropical cyclones in the wa- tropical cyclones. In general, three or four named tropi- ters to the south and southwest of Mexico. cal cyclones strike the coast of Mexico each year. Tropi- Most of the tropical cyclones this season were steered cal cyclone activity was below average in the basin com- westward and west-northwestward away from the coast pared with the mean totals for the 1966–2003 period of of Mexico, around a 500-mb ridge extending from the 15 named storms and 8 hurricanes. Of the 12 tropical Atlantic westward across northern Mexico. This feature storms that formed during the 2004 season, 6 became (Fig. 2) persisted through most of the active portion of hurricanes (Table 1; Fig. 1). Three of the hurricanes in the season and was stronger than normal, as indicated 2004 became “major,” that is, maximum 1-min average by positive 500-mb height anomalies over Mexico winds of at least 96 kt [category 3 or higher on the through the period (not shown). Saffir–Simpson hurricane scale (SSHS); Saffir (1973); One possible explanation for the below-average Simpson (1974)]. The season started early with Agatha number of tropical storms and hurricanes in 2004 is that on 22 May and ended with Lester in mid-October. His- although the ocean was a little warmer than normal in torically, the median day for formation of the first east- the genesis region south and southwest of Mexico, ern North Pacific tropical storm is 2 June. Javier was many of the developing tropical depressions and distur- the strongest hurricane of the season with peak winds bances were steered west-northwestward toward a re- of 130 kt. In addition to the 12 named cyclones in 2004, gion of cooler than normal waters. The anomalous cool there were four tropical depressions that did not reach water persisted during the season just north of 16°N tropical storm status. One of them, Sixteen-E, made and west of 112°W as indicated in Fig. 3. The cool water landfall in Baja California, Mexico. most likely inhibited additional development of the in- The formation of tropical cyclones from tropical cipient cyclones. In fact, the average lifetime of the tropical cyclones during this season was only about 4 days, about 2 days shorter than normal. In addition, the Corresponding author address: Lixion A. Avila, Tropical Pre- diction Center, National Hurricane Center, NOAA/NWS, 11691 atmosphere in the genesis region was more stable than SW 17th Street, Miami, FL 33165-2149. normal during the entire season, as shown in Fig. 4. E-mail: [email protected] Stable conditions are considered a negative factor for Unauthenticated | Downloaded 09/28/21 01:45 PM UTC MARCH 2006 ANNUAL SUMMARY 1027 TABLE 1. Eastern North Pacific basin hurricane season statistics vertical wind shear was near average during the season a for 2004. (figure not shown). Therefore, vertical shear was not Max Min likely a cause for the low number of tropical cyclones in 1-min wind pressure 2004. Name Classb Datesc (kt) (mb) Agatha H 22–24 May 50 997 2. Storm and hurricane summaries Blas T 12–15 Jul 55 991 Celia H 19–25 Jul 75 981 The National Hurricane Center (NHC) produces a Darby H 26 Jul–1 Aug 105 957 tropical cyclone “best track” database that consists of Estelle T 19–24 Aug 60 989 center positions (latitude and longitude), intensity Frank H 23–26 Aug 75 979 (maximum 1-min average sustained wind at 10 m), and Georgette T 26–30 Aug 55 995 Howard H 30 Aug–5 Sep 120 943 surface pressure every 6 h. In the eastern North Pacific Isis H 8–16 Sep 65 987 basin, the best-track data are derived mostly from esti- Javier H 10–19 Sep 130 930 mates using satellite data and applying the Dvorak Kay T 4–6 Oct 40 1005 (1984) technique. Aerial reconnaissance is rare in this Lester T 11–13 Oct 45 1000 basin. In fact, the only reconnaissance flight in 2004 was a There were no direct deaths associated with Eastern North Pa- conducted by the 53rd Weather Reconnaissance Squad- cific tropical cyclones in 2004. ron, the “Hurricane Hunters” of the U.S. Air Force b (T) Tropical Storm: wind speed of 34–63 kt. (H) Hurricane: wind Reserve Command (AFRC) during Tropical Storm speed of 64 kt or higher. Lester when the cyclone was near land. A description c Dates begin at 0000 UTC and include tropical depression stage. of the various observational data sources utilized to track tropical cyclones in this basin is given by Avila et tropical cyclone genesis since deep convection becomes al. (2003). More information about each named tropical limited. Stability is one of the input variables to the cyclone as well as the complete best track is located on National Environmental Satellite, Data, and Informa- the NHC Internet home page (http://www.nhc.noaa. tion Service (NESDIS) tropical cyclone formation pa- gov/pastall.shtml). rameter as described by De Maria et al. (2004). An- other factor that should be considered in explaining the a. Tropical Storm Agatha: 22–24 May level of tropical cyclone activity is the vertical wind A nearly stationary trough of low pressure became shear. It was found, however, that the magnitude of the established from the eastern Pacific east-northeastward FIG. 1. Eastern North Pacific tropical storm and hurricane tracks for 2004. Unauthenticated | Downloaded 09/28/21 01:45 PM UTC 1028 MONTHLY WEATHER REVIEW VOLUME 134 FIG. 2. Mean 500-mb heights for June–September 2004. Arrows mark the track of the 2004 named tropical cyclones. across Central America and portions of the Caribbean on that day. It is estimated that the cyclone reached its Sea during mid-May. This pattern resulted in a large peak intensity of 50 kt at 0000 UTC 23 May. Thereafter, area of moist southwesterly monsoon-like flow over the lower sea surface temperatures and stable air caused region. A poorly defined westward-moving tropical the cyclone to weaken gradually, and it degenerated to wave became convectively active over the eastern Ca- a remnant low by 1200 UTC 24 May. The low moved ribbean Sea on 13 May and crossed Central America little and dissipated by 0000 UTC 26 May. two days later accompanied by limited cloudiness and Special Sensor Microwave Imager (SSM/I) and thunderstorms. Once the wave reached the eastern Pa- Tropical Rainfall Measuring Mission (TRMM) images cific and combined with the trough, the convection as- of Agatha from around 1400 UTC 22 May through 0230 sociated with the wave gradually became organized, UTC 23 May revealed a ring of precipitation resem- and on 20 May, the system showed signs of cyclonic bling an eyewall. One of these images is shown in Fig. rotation. As the wave continued westward, the thun- 5. The presence of the convective ring suggests that derstorm activity became concentrated to the south- Agatha’s peak intensity was probably higher than indi- west of a developing low-level circulation center and it cated by the 35–45-kt winds suggested by the Dvorak is estimated that a tropical depression formed at 0000 estimates, although no technique is available at this UTC 22 May about 500 n mi south-southeast of Cabo San Lucas, Mexico. The depression moved slowly to- ward the northwest, and under light shear, the cyclone intensified and became a tropical storm by 1200 UTC FIG. 4. Vertical instability parameter for the eastern North Pa- cific east of 110°W, for the May–November 2004 period. This is FIG. 3. SST departures from the 1968–96 long-term mean for the one of the inputs to the tropical cyclone formation parameter as June–September 2004 period. Shaded areas denote cold anoma- described by DeMaria et al. (2004). Note that the atmosphere was lies and arrows mark the track of the 2004 named tropical cy- more stable than normal throughout the season in the genesis clones. region. Unauthenticated | Downloaded 09/28/21 01:45 PM UTC MARCH 2006 ANNUAL SUMMARY 1029 creased and Blas gradually weakened due to lower sea surface temperatures. The weakening storm turned to- ward the west-northwest on 14 July. Although the cir- culation remained large and well defined, cool waters continued to take their toll on Blas and the cyclone weakened to a tropical depression by 1800 UTC 14 July.