Danny was a slow-moving category one hurricane
on the Saffir/Simpson Hurricane Scale that made landfall near the mouth
of the Mississippi River and in the Mobile Bay area. It produced enormous
amounts of rain over extreme southern Alabama.
a. Synoptic History
Like tropical cyclones Ana,
Bill, and Claudette, Danny came from a weather
system of non-tropical origin. On 13 July, a broad upper-tropospheric trough over the
southeastern United States triggered a cluster of thunderstorms over the lower
Mississippi River valley. This area of convection drifted southward over the
north-central Gulf of Mexico coastal waters, and appears to have contributed to the formation
of a small, weak surface low near the coast of Louisiana on the 14th.
Over the next couple of days, the cyclonic circulation expanded somewhat over the
northern Gulf. However, surface winds remained quite weak and the associated deep
convection was not persistent or well-organized. By 1200 UTC on 16 July, deep
convection became a little better organized near the center and the system began to
resemble a tropical cyclone. Initial Dvorak satellite classifications
were given. Observations from oil rigs and NOAA data buoys
at the same time showed that the circulation had become well-defined. These surface and near-surface
data indicated that maximum winds were near 25 knots. It is estimated that
Tropical Depression Four formed at this time
(Table 1), centered about 125 n mi south of the coast of
southwestern Louisiana. The track of the tropical cyclone is depicted in
Figs. 1a (61K GIF) and 1b (50K GIF).
Development of the system was rather slow until around 1200 UTC 17 July.
Starting around that time, the amount and organization of deep convection increased
dramatically. Data from an
Air Force Hurricane Hunter
"fixing" the center
of the cyclone at 1448 UTC on the 17th suggested that the cyclone
had reached tropical storm strength. Satellite intensity estimates
showed an increase from a T2.0 to T3.0 on the Dvorak scale in the interval from 1200 to 1800 UTC.
Danny continued to strengthen, and was a hurricane by 0600 UTC on the 18th. By this time the center
was nearing the Mississippi River delta.
While over the northern Gulf coastal area, Danny was generally located on the
southeast side of a very weak mid-tropospheric trough that was oriented from east-northeast to
west-southwest. In effect, Danny was "sandwiched" between two high pressure areas. Consequently, the
cyclone moved quite slowly in a generally east-northeastward direction. It is rather rare for
Gulf of Mexico tropical cyclones to move in this direction during the month of July.
At times, the forward motion slowed nearly to a halt.
Hurricane Danny made its first landfall, just northwest of the Mississippi River
delta near the towns of Empire and Buras, early on 18 July. Danny was a very small
hurricane, and significant effects were confined to the area immediately around the
eye. Reports from the
indicated a radius of maximum
winds of eight or nine n mi. Communities from Port Sulphur southeastward to Venice,
Louisiana probably experienced hurricane force winds (the Venice ASOS site lost
power after reporting wind gusts to 38 knots a couple of hours before
the closest approach of the hurricane's center).
After passing over extreme southeastern Louisiana, the center of Danny was back
over the Gulf of Mexico, south of the coast of Mississippi, during the day on 18 July.
There was a little more strengthening, and Danny reached its peak intensity of
70 knots with a minimum central pressure of 984 mb. The slow-moving
hurricane wobbled to the east, then north-northeastward, bringing the eye to the mouth of Mobile Bay,
near Fort Morgan, Alabama, just before dawn on the 19th. The
eyewall and western edge
of the eye passed over Dauphin Island, where sustained hurricane-force winds and
torrential rains were experienced. After drifting over extreme southern Mobile Bay,
the center plodded eastward, practically stalled, and finally crossed the coast on the
southeast shore of the bay near Mullet Point, Alabama around midday on the 19th.
Danny continued to move erratically, toward the southeast over extreme southeast
Alabama, while weakening to a tropical storm by 0000 UTC on the 20th. The
weakening cyclone then turned northward, passing over the extreme northwest Florida
panhandle. Danny, weakened to a depression by 1800 UTC on the 20th, moved north
to northeastward over Alabama for two days.
Satellite images showed that Danny, although very weak at the surface, still had a
well-defined cyclonic cloud signature as it moved eastward over northern Georgia and
South Carolina on 22-23 July. The low pressure system moved east-northeastward
over North Carolina on the morning of the 24th. Around midday, as the center neared
the Atlantic seaboard near the North Carolina/Virginia border, the cyclone began
strengthening -- while accelerating in forward speed. The fact that Danny was re-intensifying
while still partially over land suggests that it may have been deriving
energy from a baroclinic source. A front was situated just to the north of the cyclone
around this time. Winds around Danny were already back to tropical storm force as
the center moved back over water around 1900 UTC on the 24th.
Just when it looked as if it were racing safely away from the coast, the storm
turned north-northeastward, and slowed dramatically, as it appeared to be drawn in toward a
middle- to upper-tropospheric cyclone over the northeastern United States. This
motion brought Danny to about 25 n mi southeast of Nantucket Island, Massachusetts,
around 0000 UTC 26 July. After buffeting southeastern Massachusetts, Danny lost its
remaining tropical characteristics, and turned out to sea -- for good. The cyclone was
absorbed in a frontal zone over the north Atlantic by 1800 UTC on 27 July.
b. Meteorological Statistics
Figures 2 (24K GIF)
and 3 (28K 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 from the U.S. Air Force Reserves (the
(from the Tropical Analysis and Forecast Branch, TAFB, the
Synoptic Analysis Branch, SAB, and the
U.S. Air Force Global Weather Center, AFGWC)
using satellite imagery, and fixes from synoptic weather map analyses.
flew a total of 11 missions into Danny, 10 in the Gulf of
Mexico ( just inland along the Gulf coast) and one in the Atlantic. Just prior to landfall
near the mouth of the Mississippi River early on 18 July, the
reported maximum flight-level (1500-foot) winds of 80 knots.
At about the same time, ten-minute average winds of 55 knots,
with gusts to 83 knots, were reported at Grand
Isle, Louisiana. Maximum winds reported by the
were 82 knots
(at 1500 feet) at 1449 UTC 18 July. The minimum central pressure recorded by the
aircraft was 984 mb at 2325 UTC on the 18th, and again at 1142, 1259, and 1410 UTC
on the 19th.
The Dauphin Island C-MAN site, on the west end of the island, measured
10-minute average winds of 65 knots at 1145 UTC 19 July
and gusts to 88 knots 21
minutes earlier. Interestingly, the Mobile WSR-88D radar showed that around these
times the strongest eyewall convection was occurring in this vicinity over the
southwest quadrant of the hurricane. At 1139 UTC, aircraft reported maximum winds
of 64 knots at the 850 mb flight level in the southwest quadrant.
Thus, surface winds and flight-level winds were about the same in this
highly convective regime of the hurricane.
True to form for a slow-moving hurricane, rainfall totals over extreme southern
Alabama were gigantic. Doppler radar estimates suggested maximum storm total
precipitation amounts to around 43 inches near Dauphin Island. Recent studies
indicate that a new reflectivity vs. rainfall relationship for tropical cyclones, used with
the Mobile radar, gives a rather accurate estimate of the actual precipitation. A
rainfall total of 36.71 inches was measured at the Dauphin Island Sea Lab observing
site. To the author's knowledge, this is the largest hurricane-related rainfall ever
recorded in the state of Alabama, and one of the largest ever measured in the United
States. Experience has shown that in the high wind regime of a hurricane, rain gauges
do not capture all of the rainfall; so, this amount is probably an underestimate of the
total. Fortunately, most of the extreme precipitation amounts occurred in areas near
the coast or over water, near southwestern Mobile Bay. This helped to limit the
amount of flooding, which would have been disastrous if rains of such magnitude had
occurred farther inland. Nonetheless, there was some significant inland flooding along
the path of Danny, notably in Charlotte, North Carolina, where rainfall totals of 8 to
12 inches where recorded. The resulting floods caused three deaths (see next section).
Storm tides of generally two to five feet
occurred from the Florida/Alabama border
to Dauphin Island. A maximum storm tide of 6.54 feet was reported along Highway
182W, about midway between Gulf Shores and Fort Morgan. This exceptionally high
water mark may have been the combined result of storm surge
and wave action. In the upper part of Mobile Bay, offshore winds blew water out of the bay so
that tides were two feet below normal. Observers reported that the bay had never been so low
and that, except for the river channels, one could have walked across the bay.
Danny spawned tornadoes in Orange Beach and Alabama Port, Alabama. Farther
inland, a severe thunderstorm cell in Danny's circulation produced five tornado
touchdowns in Lexington (causing one fatality; see next section), Richland (two
touchdowns), Kershaw, and Chesterfield Counties of South Carolina. A small, weak
tornado was reported in Abbeville County, South Carolina. A few hours before Danny
moved into the Atlantic, tornadoes touched down in the South Norfolk section of
Chesapeake, Virginia and also in downtown Norfolk.
In southeastern Massachusetts, the strongest winds were experienced on Nantucket
Island. There, sustained tropical storm force winds, with gusts of
50 to 60 knots, were experienced.
Table 2 lists a selection of surface observations
taken during Danny.
c. Casualty and Damage Statistics
Danny was directly responsible for four deaths. A man was killed when he was
caught at sea on his sailboat, off the Alabama coast near Fort Morgan. A woman was
killed by a tornado which tore apart her duplex in Lexington County, South Carolina.
In Charlotte, North Carolina (Mecklenberg County), a girl drowned when floodwater
swept her into a creek, and a woman was drowned in her car by floodwater. Five
additional fatalities are indirectly associated with Danny. A man died of a heart attack
while trying to secure a boat during the storm on the Alabama coast, and four people
died in storm-related traffic accidents in Georgia.
According to the American Insurance Services Group, insured losses from Danny
were about 60 million dollars. The National Hurricane Center estimates around 100
million dollars in total damage.
d. Forecast and Warning Critique
Excluding the tropical depression stage, the average official track forecast errors for
Danny were 45 n mi at 12 hr, 102 n mi at 24 hr, 139 n mi at 36 hr, 150 n mi at 48 hr,
and 147 n mi at 72 hr. These are comparable to the long-term averages for 12, 24 and
36 hours, and about 17% and 46% lower than the long-term averages at 48 and 72
hours, respectively. However, the number of cases was rather small, ranging from 18
at 12 hr to only one at 72 hr.
Several of the official track forecasts made when Danny was in the Gulf of Mexico
showed a left bias. This was mainly due to a similar left bias in several of the
model predictions, which incorrectly showed landfall on the coast of Mississippi, and
very heavy rains spreading over that state. The north-northeastward turn toward Cape
Cod was not shown by the objective track prediction models or by the official forecast.
On the 16th, 17th, and early on the 18th of July, there were some fairly large
underforecasts of the intensity. Part of this was due to an underprediction of the fast
strengthening of Danny to a hurricane while it was near the coast, and part was due to
moving the cyclone inland too soon in the forecasts.
Table 3 lists the various watches and warnings
that were issued for Danny. A hurricane watch
was posted for the Louisiana, Mississippi, and Alabama coasts when
the cyclone strengthened into a tropical storm at 1500 UTC 17 July. When Danny had
strengthened to a hurricane, this watch was upgraded to a
hurricane warning at 0700
UTC 18 July, only a couple of hours before landfall in extreme southeastern Louisiana,
and 27 hours before the landfall on the coast of Alabama. The
tropical storm warning for southeastern Massachusetts
was issued a little less than 12 hours before Danny's closest point of approach to that area,
but only a couple of hours prior to the occurrence of sustained tropical storm force winds there.
Some of the information in this report came from preliminary storm reports from
National Weather Service offices in
Lake Charles and
Tallahassee, Florida, and
Taunton, Massachusetts. Dr. Stephen R. Baig
produced the track charts.