Tropical Cyclone Report

Tropical Storm Lorenzo

Lorenzo was a short-lived tropical storm with winds to 35 knots over the central north Atlantic Ocean.

a. Synoptic History

Lorenzo originated from a tropical upper tropospheric trough that had persisted over the eastern North Atlantic Ocean. On 26 October, a low-level circulation developed beneath this trough. On the next day, organized convection was sufficient to identify the system as a tropical depression, centered about 750 n mi south-southwest of the westernmost Azores. The "best track"of the tropical cyclone begins at 1200 UTC on the 27^th. A map of the best track positions is shown in Figure 1 and six-hour center positions, wind speeds, and central pressures are listed in Table 1. Time series curves of best track wind speed and pressure are shown in Figure 2 and Figure 3.

The depression moved westward, steered by a deep-layer ridge located to its north. It gradually turned northward on the 30^th, as a strong trough in the westerlies and frontal zone approached from the west. The low-level center was mostly exposed to the west of the convection until this turn when some deep convection flared up near the center. The depression is estimated to have strengthened to Tropical Storm Lorenzo early on the 30^th. Lorenzo merged with the approaching frontal zone on the 31^st, while located about 600 n mi west of the westernmost Azores.

b. Meteorological statistics

Satellite data is the primary basis for the best track values of maximum 1-minute surface wind speed and minimum central surface pressure. The satellite intensity estimates are plotted in Figure 2 and Figure 3. In addition, a QuikSCAT pass on the 30^th showed uncontaminated wind speeds to 35 knots. The ship 3ESP7 reported winds from 37 to 43 knots on the 28^th and 29^th, as it moved near the depression. However, this ship is estimated to have a positive wind speed bias of 23 knots, based on a comparison with other ship reports by the Marine Prediction Center.

c. Casualty and damage statistics

No deaths or damages are attributed to Lorenzo.

d. Forecast and warning critique

Lorenzo was a tropical storm for 30 hours and only four 12-hour forecasts and two 24-hour forecasts were verified. The few official track forecasts verified had track errors somewhat larger than the previous ten-year average official errors. The few official intensity errors were smaller than the previous ten-year averages.

Figure 1: Best track positions for Tropical Storm Lorenzo, 27-31 October 2001.

Figure 2: Best track maximum sustained surface wind speed curve for Tropical Storm Lorenzo, 27-31 October 2001, and the observations on which the best track curve is based.

Figure 3: Best track minimum central pressure curve for Tropical Storm Lorenzo, 27-31 October 2001, and the observations on which the best track curve is based.