Tropical Cyclone Report

Tropical Storm Arlene

Arlene made landfall on the Florida Panhandle just west of Pensacola, causing minimal damage.

a. Synoptic History

The origin of Arlene is not clear but it appears to be associated with the interaction of the Intertropical Convergence Zone (ITCZ) and a tropical wave. The ITCZ near 90°W was centered over Central America during the first few days of June. This zone became a little more convectively active when a westward moving tropical wave moved across Central America on 5-6 June. Thereafter, another tropical wave, this one a little more vigorous, moved across the western Caribbean Sea on 7-8 June, resulting in pressure falls and a significant increase in cloudiness and thunderstorms over the region. Vertical wind shear gradually relaxed as an upper-level ridge developed over the large area of disturbed weather. The system became better organized and it is estimated that a tropical depression formed at 1800 UTC 8 June just north of the northeastern coast of Honduras. Very deep convection developed in cyclonically curved bands to the north and east of the center of circulation and the depression became Tropical Storm Arlene at 0600 UTC 9 June, about 150 n mi west-southwest of Grand Cayman.

Arlene began to move slowly northward with steady intensification and its center crossed western Cuba very near Cabo Corrientes with winds of 45 knots early 10 June. These winds were confined to rain bands in the eastern semicircle, primarily over water. Once in the Gulf of Mexico, Arlene moved between the north and north-northwest and continued to strengthen. The cyclone reached its peak intensity of 60 knots and a minimum pressure of 989 mb at 0100 UTC 11 June over the northeastern Gulf. Thereafter, dry air began to enter the circulation and deep convection diminished considerably, resulting in a gradual weakening. Arlene made landfall as a 50-kt tropical storm just west of Pensacola, Florida about 1900 UTC 11 June. Arlene continued to weaken as it moved northward, farther inland. It turned northeastward and became extratropical at 1800 UTC 13 June just northeast of Flint, Michigan and was absorbed by a front at 1200 UTC 14 June. The "best track" chart of the tropical cyclone's path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 1.

b. Meteorological Statistics

Observations in Arlene (Figs. 2 and 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 flight-level observations from flights of the 53rd Weather Reconnaissance Squadron of the U. S. Air Force Reserve Command and the NOAA P-3. The latter included surface wind data from the Stepped Frequency Microwave Radiometer (SFMR). 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 were also useful during Arlene. Table 2 includes ship observations with winds of at least 34 knots and Table 3 shows selected surface observations including rainfall and storm surge. The strongest 1-min sustained wind reported by a land station was 41 knots at Punta del Este, on the Isle of Youth, Cuba. The strongest gust was 52 knots and occurred at fire station at Navarre, Florida. After landfall, Arlene spread 3 to 7 inches of rain over the central and eastern United States according to data provided by the Hydrometeorological Prediction Center (HPC).

Arlene was characterized by its large circulation and the lack of inner convective core. In fact, there were various centers rotating around a larger gyre throughout the storm's lifetime. The cyclone was very asymmetric with the strongest winds confined to rain bands to the north and east of the circulation center. Only just prior to landfall, satellite pictures revealed a more symmetric cloud pattern which was more typical of a tropical cyclone.

c. Casualty and Damage Statistics

The NWS forecast office in Miami reported that a Russian exchange student died in a rip current triggered by Arlene on 10 June at Miami Beach. Reports from NWS forecast offices indicate that there was little or no damage caused by Arlene.

d. Forecast and Warning Critique

Arlene's track forecast errors were much smaller than the average official track errors for the 10-yr period 1995-2004 . The United Kingdom model (UKMET) outperformed the official forecast at all times except at 12 hours. There were just a few 96-h and no 120-h forecasts to verify. Table 4 lists the forecast errors for a selection of track forecast models. Average official intensity errors were 7, 9, 7, 9, 9 and 5 kt for the 12, 24, 36, 48, 72, and 96 h forecasts, respectively. For comparison, the average official intensity errors over the 10-yr period 1995-2004 are 6, 10, 12, 15, 18, and 20. Global models were very good in forecasting the development of a tropical cyclone in the northwestern Caribbean Sea a few days in advance.

Track models were quite clustered, reducing the uncertainty of the forecast. However, because Arlene had a large area of tropical storm force winds to the north and east of the center, the tropical storm warning area was also large. Arlene also was forecast to be very near hurricane strength and taking into consideration the general uncertainty in intensity forecasting, a hurricane warning was issued for a small portion of the area already in place tropical storm warning. A summary of the coastal watches and warnings is included in Table 5.

Acknowledgments

NWS/WFOs in Newport, Wilmington, Charleston, and Wakefield contributed many of the observations contained in this report. The highest winds observations over land were provided by Mark Sudduth and Weatherflow, Inc.

^[1]Errors given for the 96 and 120 h periods are averages over the four-year period 2001-4.

Figure 1: Selected wind observations and best track maximum sustained surface wind speed curve for Arlene, 8-13 June, 2005. Aircraft observations have been adjusted for elevation using 80%, reduction factors for observations from 1500 ft or less. Wind best track after landfall was completed using HPC estimates. Vertical black line marks the landfall time.

Figure 2: Selected wind observations and best track maximum sustained surface wind speed curve for Arlene, 8-13 June, 2005. Aircraft observations have been adjusted for elevation using 80%, reduction factors for observations from 1500 ft or less. Wind best track after landfall was completed using HPC estimates. Vertical black line marks the landfall time.

Figure 3: Selected pressure observations and best track minimum central pressure curve for Tropical Storm Arlene, 8-13 June, 2005. Pressure best after landfall was completed using HPC estimates. Vertical black line marks the landfall time.