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Preliminary Report
Hurricane Hilary
17 - 21 September 1999

Miles B. Lawrence
National Hurricane Center
1 December 1999

Hurricane Adrian
Hurricane Beatriz
Tropical Depression Three-E
Tropical Depression Four-E
Tropical Storm Calvin
Tropical Depression Six-E
Hurricane Dora
Hurricane Eugene
Tropical Depression Nine-E
Tropical Storm Fernanda
Tropical Depression Eleven-E
Hurricane Greg
Hurricane Hilary
Tropical Storm Irwin

[1999 East Pacific Hurricane Season]

Hilary briefly became a 65-knot hurricane while located about 200 n mi southwest of the southern tip of Baja California, but did not affect land.

a. Synoptic history

Hilary originated from a tropical wave that moved from west Africa to the Atlantic on 29 August. It was a weak wave with minimal organized convection as it moved across the tropical Atlantic and the Caribbean. The wave acquired some organized convection on the 10th and 11th of September while over Central America. Visible satellite imagery on the 17th showed a low-level circulation, along with some organized deep convection, and a tropical depression is estimated to have formed later that day, while centered about 475 n mi south-southeast of the southern tip of Baja California, Mexico. The best track begins on the 17th, as indicated in Table 1 which is a listing, every six hours, of best track positions, maximum one-min surface wind speeds, and minimum central surface pressure. A map of the best track positions is shown in Figure 1.

The depression was upgraded to a tropical storm on the 18th, based on the low-level center being located under deep convection. Hilary had been moving generally west-northwestward during this time as it slowly strengthened. A deepening mid- to upper-level trough approached Hilary from the northwest and the motion turned sharply toward the north-northwest late on the 19th. A banding-type eye feature, increased symmetry, and an enlarging of deep convection are the bases for upgrading Hilary to a 65-knot hurricane for a short time early on the 20th, while centered some 200 n mi southwest of the southern tip of Baja California. Later that day, the low-level center became exposed to the south of the deep convection and Hilary weakened to a tropical storm. The cyclone moved over cool water and the weakening continued. Hilary was reduced to a swirl of low clouds, devoid of deep convection on the 21st, and the best track ends about 100 n mi west of Cabo San Lazaro, Baja California.

b. Meteorological statistics

The best track pressure and wind speed time series curves are shown in Figure 2 and Figure 3, along with plots of the data on which the curves are based. Satellite-based intensity estimates are the only available data, except that the ship SALUS reported a 37-knot wind speed while located about 120 n mi east of the center at 0000 UTC on the 20th.

c. Casualties and damages

Hilary did not affect land and there are no known deaths or damages.

d. Forecast and warning critique

There were 12 forecasts made while Hilary was a tropical storm and only four of these verified at 48 hours and none verified at 72 hours. The average track forecast errors were 45 n mi at 12 hours (10 cases), 81 n mi at 24 hours (8 cases), 119 n mi at 36 hours (6 cases) and 194 n mi at 48 hours (4 cases). These errors are somewhat higher that the previous 10-year averages for the eastern Pacific basin. This is probably related to the sharp right turn described above and the resultant left bias of the official forecasts. Wind speed forecast errors were modestly small as the intensification and weakening of Hilary were well-forecast.

Figure 1. Best track positions for Hurricane Hilary, 17-21 September 1999.

Figure 2. Best track maximum 1-min sustained wind speed curve for Hurricane Hilary.

Figure 3. Best track minimum central surface pressure curve for Hurricane Hilary.

Table 1. Preliminary Best Track, Hurricane Hilary, 17-21 September 1999.
Position Pressure
Wind Speed
Lat. (°N) Lon. (°W)
17/060015.2107.1100625tropical depression
120016.2111.3100235tropical storm
120022.4114.398860tropical storm
120024.9114.6100330tropical depression
22/0000 dissipated
20/060021.6114.098765minimum pressure


Last updated February 11, 2000