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Tropical Cyclone Report
Hurricane Alberto
3 - 23 August 2000

Jack Beven
National Hurricane Center
8 December 2000

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/ 180010.818.0100725tropical depression
04 / 000011.5 20.11005 30"
04 / 060012.0 22.31004 35tropical storm
04 / 120012.3 23.81003 35"
04 / 180012.7 25.21002 40"
05 / 000013.2 26.71001 40"
05 / 060013.7 28.21000 45"
05 / 120014.1 29.8 999 45"
05 / 180014.5 31.4 994 55"
06 / 000014.5 33.2 987 65hurricane
06 / 060014.6 34.4 985 65"
06 / 120014.7 35.4 983 70"
06 / 180015.2 36.6 981 75"
07 / 000015.7 38.1 979 75"
07 / 060016.0 39.6 978 80"
07 / 120016.2 41.0 977 80"
07 / 180016.5 42.2 978 80"
08 / 000016.7 43.6 979 75"
08 / 060017.0 44.9 982 70"
08 / 120017.7 45.7 985 70"
08 / 180018.6 46.5 987 65"
09 / 000019.6 47.2 989 60 tropical storm
09 / 060020.6 48.5 992 60"
09 / 120021.9 49.9 994 55"
09 / 180023.4 51.3 991 60"
10 / 000024.8 52.6 988 65hurricane
10 / 060026.1 54.0 987 65"
10 / 120027.5 55.3 986 65"
10 / 180028.8 56.7 984 65"
11 / 000029.9 57.7 982 70"
11 / 060031.1 58.4 979 75"
11 / 120032.2 58.6 976 80"
11 / 180033.3 58.5 973 85"
12 / 000034.3 58.0 970 90"
12 / 060035.1 56.7 960100"
12 / 120035.9 55.3 950110"
12 / 180036.8 53.8 954110"
13 / 000037.4 52.0 958105"
13 / 060038.0 50.3 966 95"
13 / 120038.4 48.3 973 85"
13 / 180038.8 46.3 980 75"
14 / 000039.0 44.2 987 65"
14 / 060039.1 42.2 991 60 tropical storm
14 / 120039.1 40.6 994 55"
14 / 180039.1 39.3 997 50"
15 / 000038.9 38.51000 45"
15 / 060038.3 38.51001 45"
15 / 120037.3 38.51002 45"
15 / 180036.6 38.91002 40"
16 / 000036.1 39.41003 40"
16 / 060035.4 40.21003 40"
16 / 120034.6 41.31003 40"
16 / 180033.9 42.41002 40"
17 / 000033.4 43.51001 45"
17 / 060033.0 44.21000 45"
17 / 120033.0 44.9 998 50"
17 / 180033.0 45.8 997 50"
18 / 000033.2 46.5 995 55"
18 / 060033.6 47.1 993 55"
18 / 120034.2 47.6 991 60"
18 / 180034.7 48.0 987 65hurricane
19 / 000034.9 48.1 979 75"
19 / 060035.3 48.2 976 80"
19 / 120035.6 48.2 973 85"
19 / 180036.0 48.2 970 90"
20 / 000036.4 48.1 970 90"
20 / 060036.7 48.0 971 90"
20 / 120037.1 47.9 972 85"
20 / 180037.4 47.7 973 85"
21 / 000037.9 47.5 974 85"
21 / 060038.3 47.3 976 80"
21 / 120038.9 47.2 977 80"
21 / 180040.0 46.7 978 80"
22 / 000041.2 45.9 979 75"
22 / 060042.6 45.4 981 75"
22 / 120044.0 44.0 983 70"
22 / 180046.1 42.1 985 65"
23 / 000048.3 39.5 987 65"
23 / 060050.7 36.8 994 55tropical storm
23 / 120053.2 35.4 997 45extratropical
23 / 180057.0 34.0 997 45"
24 / 000059.5 30.3 995 40"
24 / 060062.0 25.5 992 35"
24 / 120065.5 23.0 990 35"
24 / 180068.0 20.0 992 30"
25 / 000069.0 12.5 990 30"
25 / 060070.7 4.9 994 30"
26/ 1200 dissipated
 
12 / 120035.955.3950110minimum 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)
MZYF304/060012.122.1150/441007.8
V2PA904/180013.324.8090/371005.0
Iver Pride12/060034.754.3160/391012.0
Stonewall Jackson12/090034.255.4200/431010.8
Kent Voyageur15/030036.740.7300/431014.8
Liberty Sun16/000034.539.3250/341010.6



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)
1224364872
CLIP46 (46)107 (44)175 (42)247 (40)400 (36)
GFDI32 (76)51 (74)64 (72)81 (67)134 (62)
GFDL*31 (76)48 (74)60 (71)72 (68)120 (63)
GFNI38 (53)71 (52)99 (50)130 (48)260 (44)
GFDN*34 (31)64 (30)90 (29)109 (28)179 (26)
GFUI42 (33)71 (33)101 (32)123 (31)205 (27)
GFDU*40 (33)68 (33)93 (33)115 (32)155 (30)
AVNI33 (50)57 (48)76 (46)98 (44)198 (40)
AVNO*32 (51)56 (49)78 (47)97 (45)167 (22)
BAMD34 (76)61 (74)86 (72)108 (70)192 (66)
BAMM40 (75)73 (73)104 (71)123 (69)190 (65)
BAMS52 (76)96 (74)133 (72)156 (70)201 (66)
NGPI52 (66)96 (64)135 (60)174 (52)363 (42)
NGPS*51 (38)86 (37)118 (35)135 (31)265 (26)
UKMI49 (66)79 (64)116 (62)154 (61)257 (57)
UKM*37 (35)75 (35)96 (33)134 (33)206 (30)
GUNS38 (60)64 (58)91 (54)122 (47)242 (39)
A90E40 (76)71 (74)111 (72)164 (70)330 (66)
A98E40 (76)70 (74)108 (72)160 (70)333 (66)
A9UK40 (35)74 (34)116 (33)178 (32)349 (30)
LBAR34 (76)66 (74)110 (72)165 (70)302 (66)
VBAR34 (53)63 (52)98 (51)139 (50)244 (48)
FSSE*38 (36)67 (35)108 (34)154 (33)254 (30)
 
NHC Official38 (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.



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Last updated December 15, 2000