Tropical Cyclone Report

Tropical Storm Nicholas

Nicholas was a long-lived tropical storm that remained over the Atlantic far from land.

a. Synoptic History

Nicholas developed from a tropical wave that moved westward from the coast of Africa on 9 October. A broad low pressure area formed along the wave on 10 October, and convection slowly became better organized during the following two days. It is estimated that a tropical depression formed near 0000 UTC 13 October about 790 n mi west-southwest of the southern 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 cyclone formed in an area of southerly to southwesterly vertical wind shear, and it would remain in such an environment through its lifetime. The system moved slowly west-northwestward and gradually strengthened, becoming Tropical Storm Nicholas late on 14 October. It then moved northwestward for the next three days, reaching a peak intensity of 60 kt on 17 October. A slow and erratic northward motion occurred from 18-20 October while Nicholas gradually weakened due to the shear. The storm turned west-northwestward later on 20 October and westward on 21 October. This was accompanied by slight re-intensification. Nicholas again turned northwestward on 22 October and weakening resumed. The cyclone became a depression on 23 October as it turned northward, and it became a non-convective remnant low on 24 October. The low merged with a cold front later that day, becoming extratropical about 505 n mi east-southeast of Bermuda.

The post-tropical cyclone history of Nicholas is complex. After becoming extratropical, the remnant low made a large anticyclonic loop from 24-28 October. A subsequent west-northwestward to westward motion on 28-29 October occurred while Nicholas moved along the warm front associated with a non-tropical low to its southwest. A second anticyclonic loop took place on 29-31 October, which was followed by a small cyclonic loop early on 1 November while the Nicholas low separated from the frontal system. The Nicholas remnant was finally absorbed into a non-tropical low pressure area late that day about 300 n mi south-southwest of Bermuda. This low, which developed sporadic bursts of central convection, moved westward to the Florida Peninsula on 3 November and then northwestward to the northern coast of the Gulf of Mexico on 5 November.

b. Meteorological Statistics

Observations in Nicholas (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). Microwave satellite imagery from the NOAA polar-orbiting satellites, the NASA Tropical Rainfall Measuring Mission (TRMM), the NASA QuikSCAT, and the Defense Meteorological Satellite Program (DMSP) satellites were also useful in tracking Nicholas.

Dvorak satellite intensity estimates from all agencies suggested that Nicholas could have been a hurricane near 1200 UTC 17 October. However, several microwave images made near that time showed that the cyclone was still partly sheared, with no evidence of an eye, an eyewall, or well-defined convective bands. Thus, it is estimated that Nicholas did not reach hurricane strength and that the maximum winds were 60 kt.

The remnants of Nicolas became involved in a complex weather pattern between 27 October and 1 November, and the exact time of dissipation occurred is uncertain. Operationally, the non-tropical low that crossed Florida was occasionally referred to as the remnants of Nicholas in tropical weather outlooks issued by the National Hurricane Center. Post-analysis suggests instead that this system absorbed the remnants of Nicholas.

There are no known surface observations of tropical-storm force or stronger winds associated with Nicholas.

c. Casualty and Damage Statistics

There were no reports of damages or casualties associated with Nicholas.

d. Forecast and Warning Critique

Average official track errors (with the number of cases in parentheses) for Nicholas were 39 (39), 64 (37), 95 (35), 127 (33), 171 (29), 185 (25), and 158 (21) n mi for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively¹. These errors are lower than the average official track errors for the 10-yr period 1993-2002² (45, 81, 116, 150, 225, 282, and 374 n mi, respectively), (Table 2). The track forecast errors are also lower than the errors of the Climatology-Persistence model (44, 83, 125, 171, 305, 455, and 614 n mi for the 12, 24, 36, 48, 72, 96, and 120 h forecasts, respectively) including almost 75% lower at 120 h. By this measure, the track forecasts had significant skill.

Although the track forecast errors are quite small, the slow and erratic northward motion on 18-20 October was not well forecast. The track forecasts called for a continuing northwestward motion, which led to 24 hr track forecast errors of near 125 n mi and 48 h errors of near 200 n mi during that time.

The official track forecasts were for the most part better than the model guidance. The average errors of the GFDL model were generally the lowest of the dynamical models through 48 h and were less than those of the official forecast from 24-72 h. The GFS model (AVNO) and the medium BAM (BAMM) generally were the best of the models after 72 h and showed lower mean forecast errors than the official forecasts at 48-96 h. The consensus model GUNA had lower average errors than the official forecasts for the 36-72 hr period.

Average official intensity errors were 4, 5, 5, 7, 9, 11, 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 1993-2002 are 6, 10, 13, 15, 19, 21, and 22 kt, respectively. The average intensity errors for Climatology-Persistence were 5, 7, 7, 9, 11, 15, and 20 kt, respectively. For the most part, the intensity forecasts correctly anticipated that vertical shear would restrict the development of Nicholas and eventually cause dissipation.

No watches or warnings were issued for Nicholas.

¹All forecast verifications in this report include the depression stage of the cyclone. National Hurricane Center verifications presented in these reports prior to 2003 did not include the depression stage.

²Errors given for the 96 and 120 h periods are averages over the two-year period 2001-2002.

Figure 1: Best track positions for Tropical Storm Nicholas, 13-23 October 2003.

Figure 2: Selected wind estimates/observations and best track maximum sustained surface wind speed curve for Tropical Storm Nicholas, 13-23 October 2003.Solid black bars denote wind ranges for the Hebert-Poteat subtropical cyclone technique.

Figure 3: Selected pressure estimates and best track minimum central pressure curve for Tropical Storm Nicholas, 13-23 October 2003.