Bertha was an early-season Cape Verde
Hurricane that moved across the
islands of the northeastern Caribbean Sea as a category 1 hurricane on the
Saffir/Simpson scale and made landfall on the
North Carolina coast near Wilmington as a category 2 hurricane. Bertha's
one-minute winds reached their maximum value of
100 knots on 9 July, while located to the north of
Puerto Rico. The last Hurricane to reach this strength, this early in the
Alma in 1966 (117K GIF) in the eastern Gulf
of Mexico with 110 knots. Bertha is responsible
for an estimated eight deaths and $250 million in U.S. damages.
a. Synoptic History
Bertha originated from a tropical wave
which moved from Africa to the Atlantic on 1 July. A weak circulation was first detected on
satellite imagery on 3 July, centered about 500 n mi south of the Cape Verde Islands in the far
eastern Atlantic Ocean. The track of the circulation center
begins on 5 July, when the circulation is believed to have reached the surface and become a
tropical depression, in the central tropical Atlantic.
This track is displayed in Fig. 1
(102K GIF) and listed in Table 1.
Bertha followed a fairly smooth curved path around the western periphery of the Atlantic
subtropical high pressure ridge. This ridge changed little during Bertha's existence and a weak
mid-level trough persisted in the western North Atlantic. For three days, the depression moved
toward the west-northwest at the fast forward speed of 20 to 25 knots and strengthened to a hurricane
with 1-min. maximum sustained winds of 75 knots on the 8th as the center moved
across the Leeward and Virgin Islands of the northeastern Caribbean. The center moved between
Antigua and Barbuda at 0600 UTC on the 8th, across St. Barthelemy, Anguilla, and St Martin,
just north of St. Thomas, and over the British Virgin Islands by 1800 UTC.
The track gradually turned northwestward on the 9th and maximum sustained winds reached
100 knots at 0600 UTC. Bertha was centered 120 n mi north of Puerto Rico at
this time, but earlier passed within 30 n mi of this island. The strongest winds were located in the
northeast quadrant of the hurricane and most of Puerto Rico experienced only
tropical storm conditions, except for
Culebra, over which hurricane-force winds might have occurred.
Moving northwestward at a slower forward speed of 15 to 20 knots, the center of Bertha moved
parallel to the Bahama islands, passing 40 to 60 n mi northeast of the Turks and Caicos islands,
San Salvador, Eleuthera and the Abacos. Again, the strongest winds were located to the northeast
of the center, but 65-knot sustained winds might have reached some of the
above mentioned islands.
Continuing on its gradual turn, the track became north-northwestward on the 10th and 11th and
the center moved parallel to the coast of Florida and Georgia at a distance of 150 to 175 n mi
offshore. During this time, the forward speed slowed to about 8 knots. Moving northward and
re-accelerating to a forward speed of 15 knots, Bertha made landfall at 2000 UTC on the 12th on
the coast of North Carolina, with the center crossing the coast midway between Wrightsville and
Topsail Beaches. The hurricane had been gradually weakening since its top speed of
100 knots on the 9th to 70 knots on the 11th.
Then, in 12 hours just before landfall, the winds increased to 90 knots,
which is the estimated maximum 1-min. wind speed at landfall. Bertha quickly dropped
below hurricane strength when it moved inland over eastern North Carolina.
It then moved northeastward along the U.S. east coast, producing
40 to 50 knot sustained winds over land from northern
North Carolina to New England and 60 knot winds over nearby Atlantic
waters. Bertha was declared extratropical
on the 14th when the center moved from the Maine coast to New Brunswick,
Canada. The extratropical storm brought 40 to 50 knot winds to the
Canadian Maritime Provinces and was tracked to just south of Greenland on the 17th.
b. Meteorological Statistics
Figures 2 and 3 (64K GIF) show a plot,
versus time, of the various data used to estimate the minimum central sea-level pressure and the
maximum 1-min. wind speed, 10 m above ground. Included are data from reconnaissance aircraft and
satellite Dvorak-technique wind speed estimates.
Table 2 lists selected surface observations of lowest pressure,
peak wind, storm surge and rainfall values.
Table 3 lists ship reports of 34 knots or greater that were associated with Bertha. The minimum
pressure of 960 mb occurred at 0600 UTC on the 9th and is based on a dropsonde measurement.
The best track maximum sustained wind speed of
100 knots at the same time is based on a 700-mb flight-level
wind speed of 122 knots, measured 19 n mi east-northeast of the center.
Observations are incomplete from the Leeward and Virgin Islands, but because the circular
eyewall was 20 - 30 n mi across, it is believed that hurricane
conditions with sustained wind speeds to 75 knots, could have occurred on Antigua,
Barbuda, Nevis, St. Eustatius, St. Bathelemy, Anguilla, St. Martin, and from St. Thomas northward
through the U.S. and British Virgin Islands. Experience with Hurricane Marilyn in 1995 suggests
that even higher sustained winds can occur over mountainous terrain as is found on many of these islands.
Winds of 35 to 40 knots were experienced over portions of Puerto Rico as
indicated by the San Juan observations in Table 2.
A reconnaissance aircraft flight level wind speed of 110 knots
in the northeast quadrant of the circulation several hours before landfall is the basis for estimating
sustained surface winds of 90 knots on the coast at landfall. The lowest
sea-level pressure observed at landfall was 977 mb at Surf City, North Carolina and a value of 974 mb
is assumed to be the minimum pressure at landfall.
Storm total rainfall amounts ranged from 5 to 8 inches along a coastal strip from South Carolina
Coastal storm surge flood heights, from
Florida through New England, ranged from 1 to 4 feet, but values to 5 feet were estimated on the North
Carolina coast from Cape Fear to Cape Lookout. A storm surge of 6 feet or a little higher is indicated
near Swansboro, where 5 to 6 feet of water was "inside of businesses on the waterfront".(from
Newport, North Carolina National
Weather Service Forecast Office
Preliminary Storm Report).
Seven tornadoes have been confirmed, and these occurred during the passage of an outer rain
band. There were five tornadoes in Virginia, one in North Carolina and one in Maryland.
c. Casualty and Damage Statistics
Twelve deaths have been related, in some way, to Hurricane Bertha. One, in Florida,
was from an evacuating military jet crashing into a house. One death from an auto accident
occurred in North Carolina and another drowned in rip currents. A surfer died in New Jersey.
In Puerto Rico, two died in an automobile accident and another died while surfing.
On the French half of St. Martin, one person was electrocuted and one fell off a boat.
The U.S. Virgin Islands, along with North Carolina, has been declared a federal disaster
area. Surveys indicate that Bertha damaged almost 2500 homes on St. Thomas and St. John. For
many, it was a second hit in the ten months since Hurricane Marilyn
devastated the same area.
It is likely that there was beach erosion on the north coast of the Dominican Republic as
Bertha passed to the north. The Bahamas were also affected by the weak side of the hurricane, but there
are no damage figures available from either of these locations.
The primary effects in North Carolina were to the coastal counties and included storm surge
flooding and beach erosion, roof damage, piers washed away, fallen trees, and damage to crops.
A survey indicated over 5000 homes damaged, mostly from storm surge. A
Federal Emergency Management Agency (FEMA)
estimate of the number of persons in South and North Carolina who evacuated is 750,000.
Minor wind damage and flooding also spread along the path of the storm all the way to New England.
The American Insurance Association reports an estimate of $135 million dollars in insured
property damage, primarily along coastal North Carolina. A conservative ratio between total
damage and insured property damage, compared to past land falling hurricanes, is two to one.
Then the total U.S. damage estimate is 2 times $135 million or $270 million dollars. No figures
are available from the Caribbean.
d. Forecast and Warning Critique
Bertha moved on a fairly smooth track. The average official track forecast errors for Bertha
ranged from 80 n mi at 24 hours (32 cases) to 147 n mi at 48 hours (29 cases) to 224 n mi at 72
hours (27 cases). These errors are 15 per cent, or more, lower than the previous ten-year
averages of the official track errors and are from 15 to 40 per cent lower than the CLIPER
forecast errors for the same cases.
Overall, the track model guidance also performed very well. However, the 0000 UTC Aviation
Model run on the 9th, when Bertha was located just north of Puerto Rico, (inexplicably?) showed
the track recurving significantly further east than the previous run. All of the track guidance
models that use the Aviation Model as a background environment also showed a similar track.
This resulted in rather large official track forecast errors on the 9th, with a 613 n mi 72-hour error
on the 1200 UTC forecast. The Aviation Model and some of the track guidance models
recovered to an excellent forecast only 12 hours later. Fortunately, this guidance problem
occurred three days prior to landfall in North Carolina and did not have a significant impact on
U.S. warnings or on warnings for the Bahamas.
Table 4 lists the various watches and warnings that were
issued. Hurricane warnings were issued from
Sebastian Inlet, Florida to Chincoteague, Virginia as well as for the Bahamas
and for the islands of the northeastern Caribbean Sea from Antigua through Puerto Rico.
Tropical storm warnings
were issued from Sebastian Inlet to north of Deerfield Beach, Florida and from north of
Chincoteague to Watch Hill, Rhode Island. Almost all of the U.S. east coast was involved with
some watch or warning and this is the result of the storm track's expected close passage to the
southeast U.S. coast. The hurricane watch
for the North Carolina landfall area was issued 65
hours before landfall and the hurricane warning was issued 47 hours before landfall. This is far
more than the 36- and 24-hour lead times that the National Hurricane Center strives for and is the
result of the forward motion decreasing at a faster rate than expected.
Table 4. Watch and warning summary, Hurricane Bertha, July 1996.
||Antigua, Barbuda, Nevis, Montserrat, St Kitts,
Anguilla, Saba, St Eustatius, Dominica, and Dutch St Maarten|
||Guadeloupe, St Barthelemy, French St Martin, U.S. and British Virgin Islands|
||Dominica northward to Anguilla and St Maarten|
||U.S. and British Virgin Islands and Puerto Rico|
|08/0000||tropical storm watch
||Dominican Republic from Isla Saona to Cabo Frances Viejo|
||Dominican Republic from Isla Saona to Cabo
||Turks and Caicos Islands|
||Dominican Republic from Cabo Caucedo to Monte Cristo, southeastern Bahamas|
|08/1500||hurricane warning discontinued
||Haiti from St Nicolas to border of Dominican Republic|
|hurricane warning discontinued
||Leeward Islands south and east of St Eustatius|
||Turks and Caicos Islands and southeastern Bahamas|
|hurricane warning discontinued||Leeward Islands|
|hurricane watch||central Bahamas|
|09/0100||hurricane warning discontinued
||U.S. and British Virgin Islands|
||hurricane warning discontinued||Puerto Rico|
|tropical storm warning
||Haiti from St Nicolas to border of Dominican Republic|
|hurricane watch||northwestern Bahamas|
|09/1500||watches and warnings discontinued
||Dominican Republic and Haiti|
|10/0300||tropical storm warning
||north of Deerfield Beach, FL to Brunswick, GA|
||north of Brunswick to NC/VA border including Pamlico and Albemarle Sounds|
|10/0900||hurricane warning discontinued
||Turks and Caicos Islands and southeastern Bahamas|
||Sebastian Inlet, FL to Cape Romain, SC|
|10/1800||hurricane warning discontinued
||Cape Romain to NC/VA border including Pamlico and Albemarle Sounds|
|tropical storm warning discontinued
||south of Sebastian Inlet, FL|
||NC/VA border to Chincoteague VA including southern Chesapeake Bay|
|11/0600||hurricane warning discontinued
|11/0900||hurricane warning discontinued
||south of Brunswick, GA|
|12/0900||hurricane warning discontinued
||Savannah, Ga southward|
|12/1500||tropical storm warning
||NC/VA border to Chincoteague, VA including southern Chesapeake Bay|
|12/1900||hurricane warning discontinued
||Cape Romain, SC southward|
||NC/VA border to Chincoteague, VA including the Hampton Roads area|
|tropical storm warning||north of Chincoteague, VA to Watch Hill,
RI including the lower Delaware Bay |
|tropical storm watch
||east of Watch Hill to the Merrimack River, MA|
||hurricane warning discontinued||south of Topsail Beach,
|hurricane watch discontinued||lower Chesapeake Bay|
|tropical storm warning||all of Chesapeake Bay and the lower tidal
Potomac River and all of Delaware Bay|
|13/0700||hurricane warning to
tropical storm warning
||Topsail Beach, NC to Chincoteage, VA including Albemarle and Pamlico Sounds|
|13/0900 ||hurricane warning discontined
||NC/VA border southward|
|13/1200||tropical storm warning discontinued
||south of Fenwick Island,
|13/1500||tropical storm warning discontinued||south of Brigatine, NJ and Delaware Bay|
|13/2100||tropical storm warning discontinued
||south of Fire Island, NY|
|14/0000||tropical storm warning discontinued
||south of Watch Hill, RI|
|14/0300||tropical storm warning discontinued
||remainder of U.S east coast|