Tropical Cyclone Report

Hurricane Lisa

Lisa was a long-lived tropical cyclone that reached hurricane strength north of 40°N latitude.

a. Synoptic History

Lisa developed from a tropical wave that crossed the African coast on 16 September. Early on 19 September the wave showed enough organization to warrant a Dvorak classification, and by 1800 UTC that day the system had developed into a tropical depression, about 450 n mi west-southwest of the Cape Verde Islands. The "best track" chart of the tropical cyclone's path is given in Figure 1, with the wind and pressure histories shown in Figure 2 and Figure 3, respectively. The best track positions and intensities are listed in Table 1.

The depression moved westward initially at about 10 kt. The synoptic-scale environment was not particularly favorable for development - the depression was located between Hurricane Karl about 650 n mi to its west-northwest and a large and convectively active tropical wave just a few hundred miles to its southeast. Despite outflow from Hurricane Karl impinging on the depression from the north, a small organized core developed and the depression rapidly strengthened on 20 September, becoming a tropical storm by 1200 UTC and reaching an estimated intensity of 60 kt 18 h later. The northerly shear prevailed, however, and Lisa gradually weakened over the next couple of days. Meanwhile, the wave disturbance was approaching Lisa from the east, and the two systems began a Fujiwhara interaction. Lisa turned southward on 22 September and then eastward the next day as the convection from the two systems became hard to distinguish. Although Lisa weakened to a tropical depression on 23 September, it was able to maintain a small but distinct low-level circulation throughout its merger with the disturbance. Lisa completed its cyclonic loop early on 24 September and briefly re-attained tropical storm strength before northerly shear again separated the cyclone from its deep convection.

On 25 September Lisa turned sharply northward ahead of a deep mid- to upper-level trough moving southeastward into the central Atlantic. The northerly shear abated and Lisa became a tropical storm for the third time at 0600 UTC, about 925 miles east of the Lesser Antilles. Lisa moved northward for five days as a tropical storm, nearly reaching hurricane intensity on 29 September when an upper-level trough in the westerlies cut off to the southwest of Lisa, reducing the southwesterly shear over the storm. During this time satellite imagery showed a ragged eye ringed by shallow convection. The following day Lisa crossed some cooler water upwelled by Hurricane Karl, convection diminished, and the cyclone's winds dropped to 45 kt, even though the eye feature remained distinct.

On 1 October, Lisa turned northeastward and accelerated ahead of an approaching short-wave trough in the westerlies. Southwesterly shear diminished and Lisa re-strengthened over 25°C waters. Early on 2 October, cloud tops cooled significantly around the eye and Dvorak estimates reached as high as 77 kt. Based on the satellite classifications, it is estimated that Lisa became a hurricane, after 13 days of existence as a tropical cyclone, at 0600 UTC 2 October, about 625 n mi southeast of Cape Race, Newfoundland. At this time, water temperatures under the cyclone were close to 23°C. Lisa was a hurricane for less than 12 hours before the cloud pattern began to deteriorate rapidly. Lisa lost tropical characteristics by 0600 UTC 3 October, and was absorbed into a frontal zone a few hours later, about 1000 n mi east-southeast of Cape Race.

b. Meteorological Statistics

Observations in Lisa (Figure 2 and Figure 3) include satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), the Satellite Analysis Branch (SAB) and the U. S. Air Force Weather Agency (AFWA), as well as microwave satellite imagery from NOAA polar-orbiting satellites, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, and Defense Meteorological Satellite Program (DMSP) satellites.

Lisa's estimated maximum intensity of 65 kt represents a blend of widely varying Dvorak intensity estimates on 2 October (Figure 2). As noted above, Lisa was over cool waters at this time and it is unclear whether hurricane force winds actually reached the surface. Operationally, Lisa was upgraded to a hurricane at 2100 UTC 1 October. However, a QuikSCAT pass shortly thereafter suggests that Lisa's winds were not as strong as indicated by the satellite classifications at that time, and the best track does not show Lisa becoming a hurricane until the following day. Conversely, a careful examination of QuikSCAT passes late on 28 and 29 August (Figure 2) suggests that during that period Lisa was stronger than indicated by satellite techniques.

Ship reports of winds of tropical storm force associated with Lisa are given in Table 2.

c. Casualty and Damage Statistics

There were no reports of damage or casualties associated with Lisa.

d. Forecast and Warning Critique

Average official track errors are given in Table 3. Official errors for Lisa were very close to the average official track errors for the 10-yr period 1994-2003^[1]. The GFS model performed very well for Lisa. Among the consensus models, GUNA provided better guidance than either CONU or the FSU super-ensemble (FSSE).

Average official intensity errors were 7, 9, 13, 13, 14, 15, and 15 kt for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1994-2003 are 6, 10, 12, 15, 19, 20, and 21 kt, respectively.

^[1]Errors given for the 96 and 120 h periods are averages over the three-year period 2001-3.

Figure 1: Best track positions for Hurricane Lisa, 19 Sept. - 3 Oct. 2004.

Figure 2: Selected wind observations and best track maximum sustained surface wind speed curve for Hurricane Lisa, 19 Sept. - 3 Oct. 2004. Surface observations (denoted by X's) represent QuikSCAT estimates of the maximum wind. Objective Dvorak estimates represent linear averages over a three-hour period centered on the nominal observation time.

Figure 3: Selected pressure observations and best track minimum central pressure curve for Hurricane Lisa, 19 Sept. - 3 Oct. 2004. Objective Dvorak estimates represent linear averages over a three-hour period centered on the nominal observation time.