Tropical Cyclone Report

Hurricane Juliette

Hurricane Juliette was a category 4 hurricane (on the Saffir-Simpson Hurricane Scale) that brought 80-knot winds and heavy rain to the southern Baja California peninsula of Mexico. It also caused flooding in the state of Sonora on mainland Mexico and caused two deaths.

a. Synoptic History

The tropical wave that produced Tropical Depression Nine on 19 September over the western Caribbean was also the origin of Juliette. Tropical Depression Nine dissipated over Central America on the 20^th. But its remnants and associated tropical wave continued westward over the eastern Pacific Ocean and became a depression at 0600 UTC on the 21^st, about 90 nautical miles south of the coast of Guatemala. The "best track" begins at this time. Figure 1 shows a map of the best track and Table 1 lists the best track positions, wind speeds and central pressures every six hours. Curves of wind speed and pressure versus time are shown in Figure 2 and Figure 3, along with the data on which these curves are based.

Juliette's track was generally west-northwestward from the 21^st to the 26^th, while located south of a mid-level ridge. This track was approximately parallel to the coast of mainland Mexico, and the center remained from 100 to 200 nautical miles offshore. Under a weak vertical shear environment, Juliette strengthened. It became a hurricane on the 23^rd, rapidly intensified to 115 knots with a pinhole eye on the 24th and reached 125 knots on the 25^th. Aircraft and TRMM satellite data indicate that there were several concentric eyewalls and eyewall replacement cycles during the 24^th through 27^th.

By the 26^th, a strong trough west of the U.S. west coast began digging southeastward and Juliette gradually turned toward the north and began weakening. Moving very slowly northward, the center passed just west of Cabo San Lucas on the southern tip of Baja California on the 28^th as wind speeds decreased to near 80 knots. These winds, heavy rain, and waves pounded the southern peninsula. Under increasing vertical shear and progressively cooler sea surface temperatures, Juliette moved inland on the 30^th near San Carlos on the west coast of Baja California, as a weakening 35-knot storm. It then moved over the waters of the central Gulf of California as a depression and finally dissipated on the 3^rd of October over the far northern Gulf of California.

Satellite imagery showed that clouds associated with the remnants of Juliette spread into New Mexico, Arizona, and southern California.

b. Meteorological Statistics

Observations plotted in 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), as well as flight-level and dropwindsonde observations from three flights of the 53^rd Weather Reconnaissance Squadron of the U. S. Air Force Reserve Command and from one flight of a NOAA research aircraft.

In Figure 2, it is seen that satellite objective T-number wind speed estimates were considerably higher than the reconnaissance aircraft wind speeds. On the 25^th, the highest aircraft flight-level winds reduced to a surface wind speed of 118 knots, while, at the same time, objective T-number wind speeds were 140 knots. The 125-knot best track value is a compromise between these values giving more weight to the aircraft data. This same adjustment was applied to objective T-numbers on the 25th, when there was no reconnaissance.

Whereas a number of hurricanes have had lower pressures estimated from satellite imagery, the aircraft-measured 923 millibars on the 25^th (Figure 3) is the second-lowest measured sea-level pressure on record in the northeastern Pacific Ocean. Only Hurricane Ava in June 1973 had a lower measured pressure of 915 millibars.

The highest wind observation from Baja California was 76 knots sustained with a gust to 94 knots at about 0000 UTC on the 30^th, from an automatic weather station at Cabo San Lucas. Rainfall totals include 5.35 inches on the 27^th at Santiago on the extreme southern peninsula, 6.59 inches on the 30th at Empalme in the Sonora Province on the mainland, and 8.16 inches on October 3^rd at San Felipe in the extreme northern peninsula. An unconfirmed report was received of "over a foot of rain" at Cabo San Lucas.

Ships reports of wind speeds greater than 33 knots are listed in Table 2.

The circulation became poorly defined as it moved over land on the west coast of Baja California near San Carlos on the 30th. The best track estimate of 35 knots at landfall is rather uncertain as the wind speeds were decreasing fast. Figure 1 shows a continuous depression stage track across Baja California and the northern Gulf of California on the 30^th. It is possible that the circulation dissipated over or near the southern Peninsula early on the 30th and another center formed in the northern Gulf of California later that day.

c. Casualty and Damage Statistics

Two deaths are attributed to Juliette. The Associated Press stated that a U.S. tourist surfing near the Baja California coast drowned in high seas on September 27^th. The Mexican government news agency Notimex reported that a fisherman died near Acapulco when his small open boat capsized in high seas on the 24^th.

The Notimex news agency also reported that Juliette "clobbered" the tourist resort of Cabo San Lucas, isolating it from the outside world for several days. The hurricane also caused flooding on mainland Mexico, driving more than 38,000 people from their homes in coastal areas of Sonora state.

Thunderstorm activity associated with the cyclone's remnants moved into southern California on the 30^th, knocking down trees and power lines across the Coachella Valley.

d. Forecast and Warning Critique

Average official track errors (with the number of cases in parentheses) were 33 (35), 53 (31),74 (29), 103 (27), and 145 (23) n mi for the 12, 24, 36, 48, and 72 h forecasts, respectively. These errors are lower than the average official errors for the previous 10-years (37, 68, 99, 128, and 185 n mi, respectively). Several of the track guidance models had errors even smaller than the official errors, including the AVN, UKMET, and NOGAPS models.

Average official intensity errors were 11, 15, 15, 15, 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 1991-2000 are 7, 12, 16, 19, and 21 kt, respectively. The best intensity guidance model, SHIPS, had errors of 14, 15, 14, 14, and 16 knots, respectively.

Table 3 lists the watches and warnings that were issued for Mexico.

Figure 1: Best track positions for Hurricane Juliette, 21 September- 03 October 2001.

Figure 2: Best track maximum sustained surface wind speed curve for Hurricane Juliette, 21 September-03 October 2001, and the observations on which the best track curve is based. Aircraft observations have been adjusted for elevation using 90%, 80%, and 80% reduction factors for observations from 700 mb, 850 mb, and 1500 ft, respectively. Dropwindsonde observations include actual 10 m winds (sfc), as well as surface estimates derived from the mean wind over the lowest 150 m of the wind sounding (LLM), and from the sounding boundary layer mean (MBL).

Figure 3: Best track minimum central pressure curve for Hurricane Juliette, 21 September-03 October 2001, and the observations on which the best track curve is based.