Jeanne remained over the eastern Atlantic. It brushed the Cape Verde Islands,
and also caused some gusty winds over the Azores just before losing tropical characteristics.
a. Synoptic History
Jeanne formed from a tropical wave that was slow to emerge from western Africa. The
associated disturbed weather lingered near the African coast from the 19th through the 20th of September, and gradually became better
organized. An initial Dvorak classification was made by the
Tropical Prediction Center's Tropical Analysis and Forecast Branch (TAFB) at 1800 UTC 19 September,
locating a center about 120 n mi offshore of the coast of Guinea. Only a slight increase in
organization and little motion was noted during the following 24 hours. By 0600 UTC 21 September, deep
convection had increased and it is estimated that the system had become a tropical depression,
while centered about 140 n mi southwest of the coast of Guinea-Bissau. Table 1 lists the
best track positions and intensities every six hours, and the track is plotted in
Figure 1 (36K GIF). According to National
Hurricane Center (NHC) records beginning in 1886, only Tropical Storm Christine of 1973 formed
farther east than Jeanne in the Atlantic basin.
The cyclone moved generally west-northwestward, gradually strengthening into a
tropical storm later on the 21st. Jeanne was situated in an environment of slight east to
southeasterly shear, which is typical for systems in the eastern tropical Atlantic. Early on the 22nd, Jeanne began to
intensify at a faster pace, and by 1800 UTC that day is estimated to have become a hurricane
while centered about 120 n mi southwest of the Cape Verde Islands. This was the closest point of approach to
those islands. For the next couple of days, Jeanne continued moving toward the west-northwest,
strengthening to its estimated peak intensity of 90 knots while located
about 580 n mi west of the westernmost Cape Verde Islands. The forward speed slowed, from 13-17
knots the previous couple of days, to near 10 knots, and the hurricane turned toward the northwest, and
then north, on 25-27 September. Jeanne weakened, mainly due to increased southwesterly vertical shear, on 25-26 September.
These events were likely caused by an amplifying mid- to upper-tropospheric trough located about 10 degrees of longitude to the west,
a feature which assured that Jeanne would remain in the eastern Atlantic for its life cycle.
Under the continued influence of the trough, Jeanne accelerated toward the north-northeast on 28 September.
The hurricane re-intensified somewhat, to near 80 knots,
while located about 550 n mi west-southwest of the Azores. As the system turned
toward the northeast and east-northeast on the 29th, its forward speed slowed and it weakened to a
tropical storm. Jeanne continued toward the east-northeast while gradually weakening. Around 0000
UTC 1 October, the cyclone reached the Azores, but had degenerated to a depression that was losing
tropical characteristics. After leaving the Azores, the extratropical
low moved eastward, generating an area of gale force winds until reaching the coast of Portugal just north of Lisbon around
0000 UTC 4 October. Jeanne's extratropical remnants became unidentifiable over Spain later that day.
b. Meteorological Statistics
Figures 2 (19K GIF) and 3 (18K GIF)
depict the curves of the best track 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. These consist of Dvorak-technique estimates from the
TAFB, the National Environmental Satellite, Data, and Information Service's
Satellite Analysis Branch (SAB), and the U.S.
Air Force Weather Agency (AFGWC in the figures) using satellite imagery,
and position/intensity estimates from surface synoptic data.
Jeanne's peak intensity of 90 knots on 24 September is
based on subjectively-derived Dvorak T-numbers of 5.0 from the TAFB and the
SAB. A French drifting
buoy, identifier 41599, reported winds of 060°/55 knots,
060°/48 knots, 110°/75 knots
near 23.3N 40.6W at 1000, 1100, and 1900 UTC, respectively, on 26 September. Although this buoy's data
are considered questionable, the 75 knot wind was used for the best track
intensity, since it was reported very near the center of the hurricane where a burst of deep convection
was occurring at the time. A ship, call sign GQVJ, reported winds of 170°/36
knots at 30.1N 37.9W at 1200 UTC 28 September. Another ship, with call sign C6KV2,
also reported winds of 170°/36 knots, at 32.4N 35.4W at 1800 UTC 28 September.
The island of Horta in the Azores reported wind gusts to 35 knots
around 1800 UTC 30 September.
c. Casualty and Damage Statistics
There were no known casualties or damages caused by Jeanne.
d. Forecast and Warning Critique
Table 2 lists the average track forecast errors for Jeanne for the official forecast and for
various guidance models. Official track forecast errors were, on average, less than the most recent ten-year averages.
It can be seen that the mean official errors were, in most cases, less than those from the
models. However, the U.K. Met. Office model (UKMI) forecasts had smaller average errors than the
official forecasts at all time periods. As Jeanne turned toward the north, the official forecasts called for
the system to accelerate too much in the latter part of the period, which led to some rather large 72-hour
position errors.
In the early stages of Jeanne, the NHC intensity forecasts were rather conservative, with
the intensity underpredicted by as much as 30 knots in the 36-72 hour forecasts. The strength was
slightly underforecast prior to Jeanne's second intensity peak. Otherwise, the official intensity forecasts
had a positive bias in most cases with overforecasts of maximum winds by as much as 25 knots in the
36-72 hour forecasts.
There was a statement in the NHC advisories that Jeanne could cause tropical storm
force winds in the southernmost Cape Verde Islands and in the Azores. The system passed far enough to
the south and southwest of the former islands to not seriously impact them (no reports of tropical storm
force winds), and it weakened below storm strength by the time it passed through the Azores.
![[NCEP Logo]](graphics/ncep.gif)
![[1998 Atlantic Hurricane Season]](graphics/smalllogo.gif){kind=small}
