a. Synoptic History
Hurricane Nora formed early on
the 16th of September about 250 nautical miles to the southwest of Acapulco
(Table 1 and Fig. 1a [19K GIF]).
It originated in a large area of disturbed weather that had slowly
become better organized while drifting west-northwestward during
the previous few days. Analysis of satellite pictures indicates
that this activity was likely related to a westward-moving
tropical wave that crossed
from Africa into the Atlantic hurricane basin on the 30th and 31st of August.
The northern part of the wave was associated with the formation of
Hurricane Erika in the central
tropical Atlantic, while the southern part continued westward
through the Caribbean Sea and northern South America, and arrived
in the eastern Pacific basin on 12 September.
Nora matured in an environment of relatively light wind shear, and
much of its development appears to have been related to variations
in sea-surface temperature (SST). Nora formed over very warm water
(29-30C). Deep convection quickly increased and became organized in well-defined
bands on the 16th, with Dvorak technique intensity estimates
of T2.5 forming the basis for estimating that the system became a
tropical storm at 1800 UTC on the 16th
(Figs. 2 [17K GIF] and 3 [15K GIF]).
Further strengthening occurred over the following two days. The
first signs of what would become a rather large and ragged eye were
detected in infrared satellite pictures early on the 18th. By late
that day, Nora was a hurricane with 90-kt
sustained winds.
During Nora's first few days, the winds around a mid-level high
over northern Mexico helped direct the tropical cyclone slowly
toward the west-northwest. From midday on the 18th to early on the
20th, however, Nora nearly stalled. The hurricane weakened during
that period. The height, amount, and organization of convection
decreased and the eye disappeared. The maximum wind speed is
estimated to have decreased to 65 knots.
This weakening is presumed to have occurred in response to the
hurricane's prolonged stay over waters cooled by upwelling beneath
its circulation. Analyses in this part of Nora's wake show SSTs
cooled by about 2C, on average, to about 27C.
By late on the 20th, Nora was on the move again, at 5 to 10 knots
toward the west-northwest or northwest, roughly parallel to the
southwest coast of Mexico. Nora then rapidly restrengthened. The
eye reappeared, initially with a diameter of 15 nautical miles, and
cloud tops cooled. Nora reached its peak maximum wind speed of
115 kt near 1200 UTC on the 21st.
On the 21st through the 23rd, Nora's track converged with, and then
followed, the track previously taken by Hurricane Linda
(Fig. 1b [22K GIF]).
In that area, Linda had been the strongest eastern Pacific
hurricane on record just a few weeks earlier and its circulation
had induced lower SSTs. Nora gradually weakened over Linda's wake,
with the eye temporarily broadening to a diameter of about 50
nautical miles and the eyewall becoming broken.
Estimated wind speeds decreased to about 70 knots at
1800 UTC on the 23rd.
An omega-like blocking pattern developed over the western United
States during the last week of September. This left a weakness in
the height pattern to the north of Nora and eventually a trough
with a cut-off low to the northwest of the hurricane. The track of
Nora became north-northwestward and then northward on the 24th.
This carried Nora over yet another SST anomaly, a large patch of
waters more than 2C above normal abutting the west coast of Baja
California. Nora remained over waters of at least 26C all the way
to its landfall on the morning of the 25th at Punta Euguenia and
then about 50 nautical miles south-southeast of San Fernando, Baja
California. Hence, Nora had restrengthened slightly, and then
weakened less quickly than most tropical cyclones in that area. It
was still at hurricane strength during its landfalls.
Nora was accelerating northward at landfall, steered by the flow
associated with the trough to its northwest. The center of the
cyclone crossed the Baja California peninsula at 20-25 knots and
traveled up the western shoreline of the Gulf of California. It
crossed into the United States, near the California/Arizona border,
still as a tropical storm, near 2100 UTC on the 25th. Most of the
heaviest precipitation was then located to the northeast of the
center.
Rapid weakening ensued and winds dropped to
tropical depression
strength near 0000 UTC on the 26th, when the center was located
about midway between Blythe and Needles, California. The low-level
center was moving toward the north-northeast as it degenerated
early on the 26th. A remnant circulation aloft apparently
persisted, however, and is likely to have been responsible for a
period of near hurricane-force winds observed at the
NWS Cedar City
Doppler radar, located in the mountains of southwestern Utah at an
elevation of about 10,600 feet.
The residual area of cloudiness and showers gradually became more
diffuse over the following two days while moving generally
northeastward, through portions of Utah, Colorado, Idaho and Wyoming.
b. Meteorological Statistics
Table 1
provides the post-storm "best track"
location and intensity estimates for Nora.
Figures 2 and 3
show the hurricane's estimated central pressure and maximum one-minute wind speed,
respectively, versus time and the associated satellite data.
Position and intensity estimates from satellite pictures were provided by the
Air Force Global Weather Center
(AFGWC), NOAA Tropical Analysis and Forecast Branch (TAFB)
and NOAA Synoptic Analysis Branch
(SAB).
Table 2 lists the observations
of tropical storm force winds. Most came from ships at sea.
A 39-kt 2-minute sustained wind was observed at Yuma during Nora's passage.
Such observations of tropical storm force winds are a rarity in the
United States for eastern Pacific tropical cyclones. The peak gust
observed at Yuma was 47 kt. A gust to
45 k t occurred at Ajo, AZ.
The NWS Doppler radar at Yuma showed a 40 nautical mile wide
band of hurricane force winds aloft to the east of Nora's center
near the Arizona/Sonora border near noon on the 25th. These winds
were observed at about 4-5,000 ft, could have extended to higher
altitudes, and likely were related to the patch of near-hurricane
force winds observed over the high terrain of southwestern Utah 12-18 hours later.
The Yuma radar indicated a small area with near 10 inches of
rain along the northern Gulf of California coast of Baja
California. In the United States, the 11.97 inches recorded at
the 5700 ft level in the Harquahala Mountains in Arizona was, by
far, the largest total (Table 3). More than three inches occurred
in some spots in Arizona, California, Nevada, and Utah. Some of
the amounts were comparable to the local yearly average rainfall.
c. Casualty and Damage Statistics
Two deaths were reported from Mexico in association with Nora.
One person was electrocuted by a downed power line in Mexicali.
The other fatality occurred to a diver caught in strong underwater
currents created by Nora off the coast of the San Quintin Valley.
In the United States, there were no deaths directly related to
Nora. The California Highway Patrol attributed three or four
traffic fatalities in southern California to weather.
Although Nora remained well offshore from southwestern
mainland Mexico, the Associated Press reported that waves to 16
feet hit that coastline, destroying dozens of homes. It also
destroyed the Pie de la Cuesta beaches of Acapulco.
About 350 to 400 people were made homeless by floodwaters in
the town of Arroyo de Santa Catarina in northern Baja California.
Heavy damage and flooding was reported in San Felipe, on the
northwestern shore of the Gulf of California. On the northeastern
shore, at Puerto Peñasco, Nora's winds blew down trees, billboards,
electric wires, taco stands, and ripped sheet-metal from homes.
Waves of 10 feet were reported there.
Damage totals in the United States are incomplete at this time
but media summaries of Nora included a loss to agriculture
preliminarily estimated at several hundred million dollars. About
a $30 to 40 million loss to lemon trees was estimated.
In Somerton, AZ, 10 miles south of Yuma, damage to mobile
homes and flooding was reported. About 12,000 people lost power in
Yuma.
In California, about 125,000 customers lost power in the Los
Angeles area with scattered, much smaller outages elsewhere. In
San Diego, El Centro, Palm Springs and Indio, street flooding was
reported. Winds knocked down about 16 power poles in Seeley.
The remnant circulation aloft apparently downed and/or sheared
off the tops of hundreds of large (1-2 ft diameter) trees in
southwestern Utah, mainly at elevations above 10,000 feet in the
area that includes the Dixie National Forest. Three residences in
that region were damaged by falling trees and power was disrupted.
d. Forecast and Warning Critique
Table 4 shows the average track
forecast errors of the numerical models and the NHC official forecast. On average,
the best short-term track guidance was provided by the statistical
track models run from the AVN and UKMET output (P91E and P9UK).
The best 72-hour forecasts were made by the UKMET model. The
average official forecasts were generally competitive with the best
available guidance. The NHC errors were comparable to the long-term averages,
except at 72 hours where they were about 20% larger than average.
The NHC intensity forecasts did not anticipate the variations
in strength accompanying Nora's interaction with upwelled waters.
A few forecast errors as large as 40 knots resulted. Otherwise,
errors were comparable to long-term averages (which increase to
about 20 kt at 72 hours).
Table 5 lists the tropical storm and
hurricane watches and warnings issued by the government of Mexico. Warnings for high
swells and waves were also posted for portions of the coast of Mexico.
The threat to the southwestern United States was unusual and
required an unprecedented coordination between the NHC and offices
in the NWS Western Region.
In one instance, a conference call was held with about twelve offices
(including the Salt Lake City RFC,
Western Region MSD, HPC, and Navy METOC facility in San Diego).
From the NHC perspective, the coordination was smooth and effective.
Acknowledgments
Operational assistance and data for this report were provided to the NHC by
NWS offices in Phoenix,
Tucson,
Flagstaff,
Las Vegas,
Salt Lake City,
San Diego and
Oxnard.
Table 5. Tropical Cyclone watch and warning summary, Hurricane Nora.
Date/time
(UTC) | Action | Location |
| 16/2100 | Hurricane Watch issued |
Lazaro Cardenas to Cabo Corrientes, Mexico |
| 17/0000 | Tropical Storm Warning issued |
Lazaro Cardenas to Punta Maldonado, Mexico |
| 17/2100 | Tropical Storm Warning discontinued
| Lazaro Cardenas to Punta Maldonado, Mexico |
| 18/2100 | Hurricane Watch discontinued |
Lazaro Cardenas to Cabo Corrientes, Mexico |
| 21/0900 | Hurricane Watch issued |
Revillagigedo Islands, Mexico |
| 21/1500 | Hurricane Warning issued--
replaced Hurricane Watch | Revillagigedo Islands, Mexico |
| 23/0300 |
Tropical Storm Warning issued |
Baja California south of 25N latitude |
| Hurricane Watch issued |
Baja California from north of 25N to Punta Eugenia |
| 23/2100 |
Tropical Storm Warning extended |
Baja California from Punta Eugenia southward |
| Hurricane Warning discontinued |
Revillagigedo Islands, Mexico |
| 24/0300 | Hurricane Watch extended |
Baja California from latitude 25N to Punta San Carlos |
| 24/1200 |
Hurricane Warning revised |
Baja California Pacific coast from Bahia Ballenas to Punta Santo Tomas; Baja California Gulf of
California Coast northward from Santa Rosalia |
| Tropical Storm Warning revised |
Baja California Pacific coast from Bahia Ballenas southward to latitude 24N |
| Hurricane Watch revised |
Mainland Mexico northward from Bahia Kino |
| Tropical Storm Watch issued |
Baja California from Punta Santo Tomas to Tijuana |
| 25/0300 | Tropical Storm Warning issued |
Mainland Mexico northward from Bahia Kino |
| 25/1200 | Tropical Storm Warning discontinued |
Baja California southward of line from Bahia Ballenas to Santa Rosalia |
| 25/1500 |
Hurricane Watch, Hurricane Warning
and Tropical Storm Watch discontinued | All areas |
| Tropical Storm Warning revised |
Gulf of California coast north of 30N latitude |
| 25/2100 | Tropical Storm Warning discontinued |
Gulf of California coast north of 30N latitude |
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