Edouard, the strongest tropical cyclone
of the 1996 Atlantic season, was a
prototypical Cape Verde hurricane.
It had a very long track, and maintained category three or greater intensity on the
Saffir/Simpson Hurricane Scale for nearly eight days.
Edouard brushed southeastern New England as it recurved out to sea.
a. Synoptic History
Edouard originated from a tropical wave
that was already well-marked by a spiral-shaped mass of convective clouds while moving across
western Africa on 17-18 August. The wave crossed the west coast of Africa early on the 19th,
accompanied by a 45-knot mid-tropospheric jet seen in rawinsonde data. Observations from Dakar and
nearby stations showed thunderstorms and squalls, along with 24-hour surface pressure
falls on the order of 3 to 4 mb as the wave passed. Soon after entering the eastern
tropical Atlantic, ship reports showed the presence of a large surface circulation. It is
estimated that a tropical depression
formed around 1800 UTC on 19 August, centered about 300 n mi southeast of the Cape Verde Islands,
as shown in the post-analysis "best track"
in Table 1 and Fig. 1
(71K GIF). This was the first in a series of four tropical
cyclones that would form over the eastern Atlantic from waves that moved off the west
coast of Africa during a two-week span in late August and early September of 1996.
Three of these systems (Edouard, Fran, and
Hortense) eventually became category three (or stronger) hurricanes.
Initially, it appeared that the westward-moving tropical cyclone would soon take a
northwestward turn in response to a weakness in the subtropical ridge over the eastern
Atlantic. However, the subtropical ridge remained strong enough to the north of the
system to keep it on a generally westward track into the central tropical Atlantic.
Higher-level winds favored intensification of the cyclone, as an
upper-tropospheric anticyclone became well established over the area. The system became
Tropical Storm Edouard
early on 22 August, and strengthened into a hurricane around 1200 UTC the following day,
when a banding-type eye was noted in satellite pictures.
When the hurricane neared 45W longitude on the 24th, a deep-layer cyclone to the
east of Bermuda began to create a weakness in the subtropical ridge. In response to
this, Edouard's direction of motion changed from westward to west-northwestward. Meanwhile,
intensification continued, and Edouard's winds strengthened to 100 knots
on the 24th and to 125 knots on the 25th, making it a category four hurricane.
The latter wind speed was the maximum intensity, and a similar wind speed is estimated on
the 26th and also around 0000 UTC on the 28th. From the 26th to the 28th, some
fluctuations in intensity were noted, apparently as the result of
cycles and occasional doses of stronger vertical shear over the area. Nonetheless,
Edouard maintained 115 knot or greater winds throughout the above period.
The final deepening episode in Edouard was observed late on 29-30 August. During that event,
three concentric eyewalls were indicated by aerial reconnaissance observations.
Overall, Edouard remained a powerful, 100-knot or stronger hurricane
for a very long time - from 24 August until early on 1 September.
Edouard moved relentlessly towards the west-northwest, at around 12 knots, until
the 29th of August. This track kept the hurricane well to the northeast and north of the
islands of the northeastern Caribbean Sea. On the 29th, a mid-tropospheric trough
became established near the U.S. east coast, creating a more northward steering
component for Edouard. Slowing its forward speed slightly, the hurricane turned
northwestward, and then northward, while gradually weakening. The cyclone passed
about midway between Cape Hatteras and Bermuda on 1 September, and then started
moving slightly east of north. Late on the 1st, the hurricane wobbled toward the north,
in the general direction of southeastern New England. However, early on the 2nd,
Edouard veered sharply toward the northeast, and the
center of the hurricane passed
about 75 n mi southeast of Nantucket island around 0900 UTC, the closest point of
approach to the United States. Maximum winds had diminished to near 70 knots
by that time.
Edouard weakened to a tropical storm near 0000 UTC on the 3rd, and became
extratropical shortly thereafter.
The storm's motion became east-northeastward, keeping the center south of Nova Scotia,
and, later, well offshore of Newfoundland. Edouard's remnant low was drawn around and
into the circulation of a larger extratropical cyclone on the 6th, and was absorbed by
this bigger system by 0000 UTC 7 September.
b. Meteorological Statistics
Figures 2 (34K GIF) and
3 (40K GIF) depict the curves of minimum central sea-level
pressure and maximum one-minute average "surface" (10 meters above ground level) wind speed,
respectively, as a function of time. Also plotted are the observations on which the
curves are based, consisting of aircraft reconnaissance data,
estimates using satellite imagery, and fixes
from synoptic analyses.
Most of the aircraft reconnaissance flights into Edouard were accomplished by the
of the U.S. Air Force Reserves.
The Hurricane Hunters flew 15 missions, and made 66 center fixes.
NOAA aircraft provided four additional fixes.
The highest wind speed reported was 140 knots (at 700 mb) at 0003 UTC 28 August.
Lowest central pressure reported was 934 mb at 1727 UTC 30 August. However, the
highest wind reported by aircraft around that time was 134 knots. Subjective
and objective Dvorak intensity estimates indicate that Edouard was stronger on 25-26
August, and also at 0000 UTC 28 August, than it was at the time of the minimum
aircraft-reported pressure. At the latter time, the hurricane appeared considerably less
well-organized on satellite images than on the earlier days.
Since Edouard crossed over the New York shipping channels, there was a large
number of encounters by vessels at sea with this hurricane.
Table 2 lists ship reports
of tropical storm force or greater wind speeds associated with Edouard.
The hurricane came close enough to New England to produce sustained winds of
tropical storm force at Nantucket Island and the Cape Cod area. Wind gusts to
hurricane force were reported at Nantucket. Table 3
lists selected surface observations
from Massachusetts, New Hampshire and Maine. In addition, there were unofficial
reports of wind gusts to 90 mph at Nantucket,
80 mph at Martha's Vineyard, and 77 mph
on Cape Cod.
Large swells, minor beach erosion, and some coastal flooding, presumably minor
as well, occurred along the coast from North Carolina northward through Maine.
c. Casualty and Damage Statistics
Two deaths have been directly attributed to Edouard. A 71-year old man died when
his boat capsized in heavy surf in Great Egg Harbor Inlet, south of Atlantic City, New
Jersey. A 28-year old man drowned while surfing at Lavallette, northeast of Tom's
River, New Jersey. Additionally, a 44-year old man suffered a broken neck (but
survived) while surfing near Atlantic City. Overall, the effects of Edouard on land
were apparently minor. Most of the damage was to boats at Martha's Vineyard and
d. Forecast and Warning Critique
In general, the track forecasts for Edouard were excellent. This may be attributable
to the objective guidance, which was quite accurate in most cases.
Table 4 lists the average track model and official
forecast errors for Edouard. One can see that the
average official forecast errors are spectacularly low, in comparison to the most recent
ten-year averages. The same can be said for the most oft-used objective track forecast
techniques, viz the GFDI, BAMD, and A90E (NHC90). The U.K. Met. Office model,
UKMI, also had rather low average track forecast errors.
NHC advisories had large underforecasts of intensity, up to 65 knots at 72 hours,
during the early stages of Edouard. Intensity was significantly overforecast, on the
order of 25 to 45 knots in 48 to 72 hours, on 30-31 August. Otherwise, the intensity
predictions were good.
Since the official forecast tracks were bringing Edouard close to the U.S. east coast,
and there was the usual uncertainty in these forecasts, watches and warnings were
required from the mid-Atlantic states northward. Table 5
summarizes these watches and warnings. A
was posted for portions of Rhode Island and
Massachusetts at 0900 UTC 1 September. Although sustained hurricane force winds
did not occur in these areas, sustained tropical storm force winds, with gusts to
hurricane force, were observed in the eastern end of the hurricane warning area 18 to
24 hours after the issuance of the warning. At 0900 UTC on the 2nd, the hurricane
warning was changed to a tropical storm warning
over southeastern New England, even though it was clear that Edouard was bypassing the area.
The reason for downgrading the warning (as opposed to lowering all warnings) was that Edouard
was slow to exit, and strong winds were likely to continue lashing the coast in the vicinity
of Cape Cod during the day. All U.S. warnings were dropped at 0000 UTC 3
September, by which time Edouard was nearing Nova Scotia.
Table 5. Watch and warning summary, Hurricane Edouard, August/September
|30/2100||hurricane watch and
tropical storm warning issued
||Cape Lookout, North Carolina northward to Cape Henlopen, Delaware including the Pamlico
and Albermarle Sounds|
||hurricane watch extended northward
||north of Cape Henlopen, Delaware to Plymouth, Massachusetts|
|hurricane watch and tropical storm warning discontinued
||south of Cape Charles, Virginia|
|1/0300||hurricane watch extended northward
||north of Plymouth, Massachusetts to Merrimack River, Massachusetts|
|1/0900||hurricane warning issued
||Watch Hill, Rhode Island to Merrimack River, Massachusetts|
|hurricane watch extended northward
||north of Merrimack River, Massachusetts to Eastport, Maine|
|tropical storm warning issued
||Fire Island Inlet, Long Island, New York to Watch Hill, Rhode Island including
Long Island Sound east of Port Jefferson Harbor|
|all watches and warnings discontinued
||south of Brigantine New Jersey|
|1/1500||tropical storm warning issued
||Merrimack River, Massachusetts to Eastport, Maine|
|1/2100||hurricane watch discontinued
||New Jersey Coast and Long Island west of Fire Island Inlet|
|2/0300||hurricane watch discontinued
||Long Island, Long Island Sound and the coast of New England west of Watch Hill,
||hurricane warning changed to
tropical storm warning
||Watch Hill, Rhode Island to Woods Hole, Massachusetts and from Plymouth, Massachusetts to
Merrimack River, Massachusetts|
|hurricane watch discontinued
||north of Merrimack River, Massachusetts|
hurricane warning changed to
tropical storm warning
||Woods Hole, Massachusetts to Plymouth, Massachusetts|
|watches and warnings discontinued
||west of Woods Hole, Massachusetts and north of Plymouth Massachusetts|
|3/0000||tropical storm warning discontinued
||Woods Hole, Massachusetts to Plymouth, Massachusetts|