Tropical Cyclone Report

Hurricane Elida

Hurricane Elida developed extraordinarily quickly, eventually reaching category 5 status on the Saffir-Simpson Hurricane Scale.

a. Synoptic History

Elida formed from a tropical wave that moved westward from the coast of Africa on 13 July. The system showed little development as it moved westward across the Atlantic and the Caribbean. It moved into the Eastern Pacific on 21 July and showed increasing organization the next day. Tropical Depression Six-E formed from the wave near 0600 UTC 23 July about 305 n mi south-southeast of Puerto Escondido, Mexico. The "best track" chart of the tropical cyclone's path is given in Figure 1, with the wind and pressure histories shown in Figure 2 and Figure 3, respectively. The best track positions and intensities are listed in Table 1.

The cyclone strengthened rapidly as it moved westward. It became a tropical storm near 1200 UTC 23 July and a hurricane less than 18 h later. Elida turned west-northwestward on the 24^th while continuing to rapidly deepen. It is estimated to have reached a peak intensity of 140 kt near 0600 UTC on the 25^th. Microwave satellite data indicate that Elida began formed concentric eyewalls near that time, and by the time the eyewall replacement cycle was complete the cyclone was moving over cooler sea surface temperatures. Thus, Elida began to weaken, albeit somewhat unsteadily. The hurricane turned westward later on the 25^th, then resumed a west-northwestward motion on the 26^th. This motion would continue through the 27^th as Elida became a tropical storm.

A weakness in the subtropical ridge helped the storm turn northwestward on 28 July and north-northwestward on the 29^th. It weakened to a depression on the 29^th, then became a non-convective low the next day. The low dissipated late on the 31^st about 465 n mi west of Los Angeles, California.

b. Meteorological Statistics

Observations in Elida (Figure 2 and Figure 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the U. S. Air Force Weather Agency (AFWA). Three sets of microwave data supplemented the conventional satellite fixes. First was the Special Sensor Microwave/Imager on the U. S. Department of Defense Meteorological Satellite Program (DMSP) satellites. Second was the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager flown by the National Aeronautics and Space Administration (NASA). The third was scatterometer data from the QuikSCAT satellite flown by NASA.

Many tropical cyclones undergo periods of rapid or explosive deepening. However, Elida began such intensification when it first formed as a tropical depression, which is very unusual. The best track indicates that Elida went from a 25-kt depression to a 70-kt hurricane in 30 h, and then strengthened to 140 kt during the next 24 h. Amongst other recent Eastern Pacific hurricanes, only Linda of 1997 showed a similar rate of strengthening. That storm took 36 h to develop from 25 kt to 65 kt, then strengthened to 155 kt in the ensuing 24 h. It should be noted that for both Elida and Linda there were no in situ observations to verify the satellite intensity estimates, and the apparent development rate violated the constraints built into the Dvorak technique. Thus, there is greater than normal uncertainty as to the exact deepening rates and peak intensity of these two storms.

Elida's peak intensity of 140 kt is based on data from an automated intensity estimation technique developed by the University of Wisconsin. Raw intensity data indicated a peak intensity of 138 kt from 0300-0400 UTC 25 July. The technique uses a comparison of infrared cloud temperatures of the eye and the eyewall on geostationary satellite data. Due to Elida's pinhole eye and the distance of the hurricane from the satellite sub-point it is likely that the eye temperature was incorrectly measured. This would result in an underestimated intensity. However, as noted above it is unknown if Elida strengthened as rapidly as indicated by the satellite signature. Thus, the maximum winds are set to 140 kt as a compromise between more extreme and more conservative possibilities.

The only ship to encounter Elida had the call sign H9LA (name unknown). It reported 36 kt winds and a 1008.5 mb pressure at 0000 UTC 24 July while about 200 n mi from the center. This ship also provided useful data during Elida's initial development into a tropical depression.

c. Casualty and Damage Statistics

While high swells from Elida likely affected portions of the coast of Mexico, the high winds and heavy rains stayed well offshore. There were no reports of damage or casualties.

d. Forecast and Warning Critique

Average official track errors (with the number of cases in parentheses) for Elida were 27 (23), 48 (21), 55 (19), 60 (17), and 77 (13) n mi for the 12, 24, 36, 48, and 72 h forecasts, respectively. These errors are considerably lower than the average official track errors for the 10-yr period 1992-2001 (36, 67, 97, 125, and 182 n mi, respectively), with the 48 and 72 h forecasts errors being more than 50% better than the long-term averages. These forecasts also show considerable skill, as the errors are 20-40% better than climatology-persistence (CLP5) at 12-48 h and nearly 60% better at 72 h. The NCEP global model (AVNI, AVNO) and the mean of its ensemble runs (AEMI, AEMN) also produced excellent forecasts with errors close to or slightly better that of the official. Table 2 shows the verification for the official forecast and various guidance models.

Average official intensity errors were 10, 20, 23, 20, and 19 kt for the 12, 24, 36, 48, and 72 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1992-2001 are 7, 12, 16, 18, and 21 kt, respectively. The intensity forecasts, in sharp contrast to the track forecasts, are worse than the long-term average at all times except 72 h. The forecasts also show no skill with respect to climatology-persistence. Failure to forecast either the extremely rapid strengthening to 140 kt - a chronic problem- or the quick weakening after peak intensity are the reasons for the large errors.

Watches or warnings were neither required nor issued for Elida.

Figure 1: Best track positions for Hurricane Elida, 23 - 30 July 2002.

Figure 2: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Elida, 23 - 30 July 2002. Objective Dvorak estimate is for a 1-hr period

Figure 3: Selected pressure observations and best track minimum central pressure curve for Hurricane Elida, 23 - 30 July 2002. Objective Dvorak estimate is for a 1-hr period.