Alberto was a long-lived Cape Verde hurricane that remained at sea through
its lifetime. It is the longest-lived Atlantic tropical cyclone to form in
August, and the third-longest-lived of record in the Atlantic. Alberto's
track included intensifying into a hurricane three times, a large
anticyclonic loop that took five days, and extratropical transition near
53°N.
a. Synoptic history
A well-developed tropical wave was observed in satellite imagery over
central Africa on 30 July. This system progressed steadily westward and
moved off the coast on 3 August. Development occurred quickly upon reaching
the Atlantic, and the wave became Tropical Depression Three at 1800 UTC that
day (Figure 1 and Table 1).
The cyclone moved west-northwestward at 15-20
kt and became Tropical Storm Alberto early the next day. Alberto continued
to strengthen and reached hurricane status early on the 6th.
This was coincident with a brief westward turn. The hurricane resumed a
west-northwestward motion later that day, which continued as Alberto reached
a first peak in intensity of 80 kt on the 7th.
A strong upper-level low developed west and southwest of Alberto on 7-8
August. This caused an increase in vertical shear, a northwestward turn on
the 8th, and weakening to a tropical storm on the 9th.
Alberto continued quickly northwestward on the 10th while it
regained hurricane strength. A gradual curve northward and
north-northeastward through a break in the subtropical ridge occurred on
11-12 August. Alberto passed about 300 n mi east of Bermuda on the
11th. The hurricane reached its second and greatest peak
intensity of 110 kt on the 12th, when a 50 n mi wide eye was
present. Increasing upper level westerlies caused weakening on the
13th and 14th as Alberto moved east-northeastward,
with the cyclone losing most of its convection as it became a tropical
storm on the 14th.
A westerly trough that had been guiding Alberto outran the storm, and strong
ridging developed to the north and west. This caused Alberto to turn
southward on 15 August, southwestward on 16 August, and westward on 17
August. The storm started to re-intensify on the 17th, and it
regained hurricane status for the third time the next day. A third peak
intensity of 90 kt, along with a 60 n mi wide eye, occurred on the
20th. The hurricane completed its loop during this period,
turning northwestward on the 18th, northward on the
19th, and north-northeastward on the 20th
and 21st.
Weakening and acceleration occurred on 22 August, and Alberto again weakened
to a tropical storm before becoming extratropical the next day.
Extratropical Alberto continued north-northeastward, passing near Iceland on
the 24th. Winds dropped below gale force as the increasingly
poorly-defined center turned east-northeastward on the 25th, and
Alberto finally dissipated about 75 n mi east of Jan Mayen Island later that
day.
b. Meteorological statistics
Table 1 shows the best track positions and
intensities for Alberto, with the
track plotted in Figure 1.
Figure 2 and Figure 3 depict the
curves of minimum
central sea-level pressure and maximum sustained one-minute average
"surface" (10 m above ground level) winds, respectively, as functions of
time. These figures also contain the data on which the curves are based:
satellite-based Dvorak technique intensity estimates from the Tropical
Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) of
the National Environmental Satellite Data and Information Service
(NESDIS), and the Air Force Weather Agency (AFWA).
Other data were scarce. Alberto was far from land, and no reconnaissance
flights were made. Only a few ships encountered the storm. A ship with the
call sign MZYF3 (name unknown) reported 44 kt winds and a
1007.8 mb pressure at 0600 UTC 4 August; this was the basis for upgrading
the cyclone to a tropical storm. A drifting buoy near the center reported 78
kt at 0900 UTC 8 August, while another drifting buoy reported 93 kt at 0900
UTC 10 August; however, the reliability of these measurements is suspect.
Yet another drifting buoy just south of the center reported a 991.8 mb
pressure near1800 UTC 11 August. Table 2 contains
selected ship reports of observations of tropical storm-force winds from
Alberto.
There is one notable ship report not included in
Table 2. The
Conti Sydney (call sign DEHU) reported 34 kt at 0600 UTC
3 August as the pre-Alberto disturbance was moving off the African coast.
This suggests Alberto may have become a tropical storm earlier than
indicated in the best track. This observation is not supported by
satellite intensity estimates.
c. Casualty and damage statistics
The National Hurricane Center has received no reports of damage or
casualties.
d. Forecast and warning critique
Table 3 shows the average track forecast errors
during Alberto, including the official forecast error, the 10-year average
forecast error, and the track guidance errors. The official forecast errors
were generally close to the 10-year average, being a little less than the
average from 12-48 h and a little greater than the average at 72 hr. The
forecasts were also better than climatology and persistence (CLIPER or CLIP
in the table) and thus showed skill. However, many of the numerical guidance
models made better forecasts than the official. The most notable was the
GFDL, which had errors of 31, 48, 60, 72, and 120 n mi at 12, 24, 36, 48,
and 72 h respectively.
There were two periods where the official forecasts were far worse than
average. The first was from 0000-1800 UTC 8 August, where four consecutive
72 h forecasts had errors greater than 500 n mi. This was due to the
official forecasts calling for a west-northwestward motion while Alberto
actually turned northwestward at 16-20 kt. The second was from 1200 UTC 11
August to 1200 UTC 12 August, where five consecutive 72 h forecasts had
errors in excess of 600 n mi, including one of 939 n mi. This was due to the
official forecast calling for a fast east-northeastward motion though the
period where Alberto actually began to loop. Figure 4 shows the guidance for
0000 UTC 12 August. Note that the guidance is somewhat split into two
clusters - a faster and somewhat further north set and a slower set and
somewhat further south set. The official forecasts followed the former set,
while the latter, though not perfect, was more accurate.
The impact of the second set of poor forecasts can be illustrated in two
ways. First, if the 939 n mi 72 h forecast error had actually been the
normal 235 nm forecast error, that by itself would have reduced the over 72
h average error for Alberto by 10 n mi. If the five consecutive forecast
errors in excess of 600 n mi had been half of their actual magnitude (which
would still be worse than average forecasts), the overall 72 h average error
for Alberto would have been reduced by 30 n mi. Peliminary computations
suggest that this second set of errors had a large influence on the annual
forecast errors for the official forecasts.
The official intensity forecast errors for Alberto were 5, 7, 8, 11, and 14
kt for 12, 24, 36, 48, and 72 h. This was better than the 10-year average
of 7, 11, 13, 16, and 19 kt at those times. The forecasts showed a slight
negative bias from 24-72 h. The largest intensity forecast errors on 10-11
August were due to underforecasting intensification as Alberto became a major
hurricane.
No watches or warnings were necessary for Alberto.
Acknowledgements
Joe Sienkiewicz of the Marine Prediction Center provided the track for the
extratropical stage. James Franklin created several of the figures.
Table 1.
Best track, Hurricane Alberto, 3 - 23 August 2000.
Date/Time (UTC) | Position |
Pressure (mb) |
Wind Speed (kt) | Stage |
Lat. (°N) | Lon. (°W) |
03/ 1800 | 10.8 | 18.0 | 1007 | 25 | tropical depression |
04 / 0000 | 11.5 | 20.1 | 1005 | 30 | " |
04 / 0600 | 12.0 | 22.3 | 1004 | 35 | tropical storm |
04 / 1200 | 12.3 | 23.8 | 1003 | 35 | " |
04 / 1800 | 12.7 | 25.2 | 1002 | 40 | " |
05 / 0000 | 13.2 | 26.7 | 1001 | 40 | " |
05 / 0600 | 13.7 | 28.2 | 1000 | 45 | " |
05 / 1200 | 14.1 | 29.8 | 999 | 45 | " |
05 / 1800 | 14.5 | 31.4 | 994 | 55 | " |
06 / 0000 | 14.5 | 33.2 | 987 | 65 | hurricane |
06 / 0600 | 14.6 | 34.4 | 985 | 65 | " |
06 / 1200 | 14.7 | 35.4 | 983 | 70 | " |
06 / 1800 | 15.2 | 36.6 | 981 | 75 | " |
07 / 0000 | 15.7 | 38.1 | 979 | 75 | " |
07 / 0600 | 16.0 | 39.6 | 978 | 80 | " |
07 / 1200 | 16.2 | 41.0 | 977 | 80 | " |
07 / 1800 | 16.5 | 42.2 | 978 | 80 | " |
08 / 0000 | 16.7 | 43.6 | 979 | 75 | " |
08 / 0600 | 17.0 | 44.9 | 982 | 70 | " |
08 / 1200 | 17.7 | 45.7 | 985 | 70 | " |
08 / 1800 | 18.6 | 46.5 | 987 | 65 | " |
09 / 0000 | 19.6 | 47.2 | 989 | 60 | tropical storm |
09 / 0600 | 20.6 | 48.5 | 992 | 60 | " |
09 / 1200 | 21.9 | 49.9 | 994 | 55 | " |
09 / 1800 | 23.4 | 51.3 | 991 | 60 | " |
10 / 0000 | 24.8 | 52.6 | 988 | 65 | hurricane |
10 / 0600 | 26.1 | 54.0 | 987 | 65 | " |
10 / 1200 | 27.5 | 55.3 | 986 | 65 | " |
10 / 1800 | 28.8 | 56.7 | 984 | 65 | " |
11 / 0000 | 29.9 | 57.7 | 982 | 70 | " |
11 / 0600 | 31.1 | 58.4 | 979 | 75 | " |
11 / 1200 | 32.2 | 58.6 | 976 | 80 | " |
11 / 1800 | 33.3 | 58.5 | 973 | 85 | " |
12 / 0000 | 34.3 | 58.0 | 970 | 90 | " |
12 / 0600 | 35.1 | 56.7 | 960 | 100 | " |
12 / 1200 | 35.9 | 55.3 | 950 | 110 | " |
12 / 1800 | 36.8 | 53.8 | 954 | 110 | " |
13 / 0000 | 37.4 | 52.0 | 958 | 105 | " |
13 / 0600 | 38.0 | 50.3 | 966 | 95 | " |
13 / 1200 | 38.4 | 48.3 | 973 | 85 | " |
13 / 1800 | 38.8 | 46.3 | 980 | 75 | " |
14 / 0000 | 39.0 | 44.2 | 987 | 65 | " |
14 / 0600 | 39.1 | 42.2 | 991 | 60 | tropical storm |
14 / 1200 | 39.1 | 40.6 | 994 | 55 | " |
14 / 1800 | 39.1 | 39.3 | 997 | 50 | " |
15 / 0000 | 38.9 | 38.5 | 1000 | 45 | " |
15 / 0600 | 38.3 | 38.5 | 1001 | 45 | " |
15 / 1200 | 37.3 | 38.5 | 1002 | 45 | " |
15 / 1800 | 36.6 | 38.9 | 1002 | 40 | " |
16 / 0000 | 36.1 | 39.4 | 1003 | 40 | " |
16 / 0600 | 35.4 | 40.2 | 1003 | 40 | " |
16 / 1200 | 34.6 | 41.3 | 1003 | 40 | " |
16 / 1800 | 33.9 | 42.4 | 1002 | 40 | " |
17 / 0000 | 33.4 | 43.5 | 1001 | 45 | " |
17 / 0600 | 33.0 | 44.2 | 1000 | 45 | " |
17 / 1200 | 33.0 | 44.9 | 998 | 50 | " |
17 / 1800 | 33.0 | 45.8 | 997 | 50 | " |
18 / 0000 | 33.2 | 46.5 | 995 | 55 | " |
18 / 0600 | 33.6 | 47.1 | 993 | 55 | " |
18 / 1200 | 34.2 | 47.6 | 991 | 60 | " |
18 / 1800 | 34.7 | 48.0 | 987 | 65 | hurricane |
19 / 0000 | 34.9 | 48.1 | 979 | 75 | " |
19 / 0600 | 35.3 | 48.2 | 976 | 80 | " |
19 / 1200 | 35.6 | 48.2 | 973 | 85 | " |
19 / 1800 | 36.0 | 48.2 | 970 | 90 | " |
20 / 0000 | 36.4 | 48.1 | 970 | 90 | " |
20 / 0600 | 36.7 | 48.0 | 971 | 90 | " |
20 / 1200 | 37.1 | 47.9 | 972 | 85 | " |
20 / 1800 | 37.4 | 47.7 | 973 | 85 | " |
21 / 0000 | 37.9 | 47.5 | 974 | 85 | " |
21 / 0600 | 38.3 | 47.3 | 976 | 80 | " |
21 / 1200 | 38.9 | 47.2 | 977 | 80 | " |
21 / 1800 | 40.0 | 46.7 | 978 | 80 | " |
22 / 0000 | 41.2 | 45.9 | 979 | 75 | " |
22 / 0600 | 42.6 | 45.4 | 981 | 75 | " |
22 / 1200 | 44.0 | 44.0 | 983 | 70 | " |
22 / 1800 | 46.1 | 42.1 | 985 | 65 | " |
23 / 0000 | 48.3 | 39.5 | 987 | 65 | " |
23 / 0600 | 50.7 | 36.8 | 994 | 55 | tropical storm |
23 / 1200 | 53.2 | 35.4 | 997 | 45 | extratropical |
23 / 1800 | 57.0 | 34.0 | 997 | 45 | " |
24 / 0000 | 59.5 | 30.3 | 995 | 40 | " |
24 / 0600 | 62.0 | 25.5 | 992 | 35 | " |
24 / 1200 | 65.5 | 23.0 | 990 | 35 | " |
24 / 1800 | 68.0 | 20.0 | 992 | 30 | " |
25 / 0000 | 69.0 | 12.5 | 990 | 30 | " |
25 / 0600 | 70.7 | 4.9 | 994 | 30 | " |
26/ 1200 | | dissipated |
|
12 / 1200 | 35.9 | 55.3 | 950 | 110 | minimum pressure |
Table 2.
Selected ship observations of tropical storm or greater winds associated
with Hurricane Alberto, 3-23 August 2000.
Ship Name or Call Sign
|
Date/ Time (UTC) |
Lat. (°N) |
Lon. (°W) |
Wind dir/speed (deg/kt) |
Pressure (mb) |
MZYF3 | 04/0600 | 12.1 | 22.1 | 150/44 | 1007.8 |
V2PA9 | 04/1800 | 13.3 | 24.8 | 090/37 | 1005.0 |
Iver Pride | 12/0600 | 34.7 | 54.3 | 160/39 | 1012.0 |
Stonewall Jackson | 12/0900 | 34.2 | 55.4 | 200/43 | 1010.8 |
Kent Voyageur | 15/0300 | 36.7 | 40.7 | 300/43 | 1014.8 |
Liberty Sun | 16/0000 | 34.5 | 39.3 | 250/34 | 1010.6 |
Table 3.
Preliminary track forecast evaluation for Hurricane Alberto - heterogeneous
sample. Errors in nautical miles for tropical storm and hurricane stages
with number of forecasts in parentheses. Numbers in bold type represent
forecast which were better than the official forecast.
Forecast Technique |
Period (hours) |
12 | 24 | 36 | 48 | 72 |
CLIP | 46 (46) | 107 (44) | 175 (42) | 247 (40) | 400 (36) |
GFDI | 32 (76) | 51 (74) | 64 (72) | 81 (67) | 134 (62) |
GFDL* | 31 (76) | 48 (74) | 60 (71) | 72 (68) | 120 (63) |
GFNI | 38 (53) | 71 (52) | 99 (50) | 130 (48) | 260 (44) |
GFDN* | 34 (31) | 64 (30) | 90 (29) | 109 (28) | 179 (26) |
GFUI | 42 (33) | 71 (33) | 101 (32) | 123 (31) | 205 (27) |
GFDU* | 40 (33) | 68 (33) | 93 (33) | 115 (32) | 155 (30) |
AVNI | 33 (50) | 57 (48) | 76 (46) | 98 (44) | 198 (40) |
AVNO* | 32 (51) | 56 (49) | 78 (47) | 97 (45) | 167 (22) |
BAMD | 34 (76) | 61 (74) | 86 (72) | 108 (70) | 192 (66) |
BAMM | 40 (75) | 73 (73) | 104 (71) | 123 (69) | 190 (65) |
BAMS | 52 (76) | 96 (74) | 133 (72) | 156 (70) | 201 (66) |
NGPI | 52 (66) | 96 (64) | 135 (60) | 174 (52) | 363 (42) |
NGPS* | 51 (38) | 86 (37) | 118 (35) | 135 (31) | 265 (26) |
UKMI | 49 (66) | 79 (64) | 116 (62) | 154 (61) | 257 (57) |
UKM* | 37 (35) | 75 (35) | 96 (33) | 134 (33) | 206 (30) |
GUNS | 38 (60) | 64 (58) | 91 (54) | 122 (47) | 242 (39) |
A90E | 40 (76) | 71 (74) | 111 (72) | 164 (70) | 330 (66) |
A98E | 40 (76) | 70 (74) | 108 (72) | 160 (70) | 333 (66) |
A9UK | 40 (35) | 74 (34) | 116 (33) | 178 (32) | 349 (30) |
LBAR | 34 (76) | 66 (74) | 110 (72) | 165 (70) | 302 (66) |
VBAR | 34 (53) | 63 (52) | 98 (51) | 139 (50) | 244 (48) |
FSSE* | 38 (36) | 67 (35) | 108 (34) | 154 (33) | 254 (30) |
|
NHC Official | 38 (76) | 71 (74) | 100 (72) | 137 (70) | 249 (66) |
NHC Official 10-Year Average (1990-1999) | 46 (2057) | 85 (1842) | 122 (1650) | 158 (1471) | 235 (1165) |
*Output from these models was unavailable at time of forecast issuance.
Figure 1.
Best track for Hurricane Alberto, 3-23 August 2000.
Figure 2.
Best track minimum central pressure curve for Hurricane Alberto, 3-23 August
2000.
Figure 3.
Best track maximum sustained 1-minute 10 meter wind speed curve for
Hurricane Alberto, 3-23 August 2000.
Figure 4.
Track guidance for Hurricane Alberto at 0000 UTC 12 August. Best track line
marked by hurricane and tropical storm symbols.