Tag Archives: Tropical Storm Arlene

Tropical Depression Two Strengthens to Tropical Storm Arlene

Former Tropical Depression Two strengthened to Tropical Storm Arlene over the eastern Gulf of Mexico on Friday afternoon. At 2:00 p.m. EDT on Friday the center of Tropical Storm Arlene was located at latitude 26.7°N and longitude 86.2°W which put it about 265 miles (425 km) west of Ft. Meyers, Florida. Arlene was moving toward the south at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1002 mb.

An Air Force Reserve Hurricane Hunter reconnaissance plane found sustained wind speeds to tropical storm force in the northeastern part of former Tropical Depression Two on Thursday afternoon and the National Hurricane Center upgraded the system to Tropical Storm Arlene. The distribution of thunderstorms in Tropical Storm Arlene was asymmetrical. Many of the thunderstorms were occurring in bands in the northeastern quadrant of Arlene’s circulation. Bands in the other parts of the tropical storm consisted primarily of showers and lower clouds. Storms near the center of Arlene generated upper level divergence that pumped mass away to the northeast of the tropical storm. Winds to tropical storm force extended out 65 miles (105 km) in the northeastern quadrant of Tropical Storm Arlene. The winds in the other parts of Arlene were blowing at less than tropical storm force.

Tropical Storm Arlene will move into an environment that will become unfavorable for intensification during the next 24 hours. Arlene will move over water where the Sea Surface Temperatures are near 27˚C. However, Tropical Storm Arlene will move under the southern part of an upper level trough over the eastern Gulf of Mexico. The upper level trough will produce westerly winds that will blow toward the top of Arlene’s circulation. Those winds will cause the vertical wind shear to increase. Drier air to the north and west of Tropical Storm Arlene will continue to inhibit the formation of thunderstorms in the western part of Arlene. The vertical wind shear and the drier air are likely to cause Tropical Storm Arlene to start to weaken during the next 24 hours.

Tropical Storm Arlene will be south of a large surface high pressure system over the eastern U.S. The high pressure system will move south on Friday and it will push Tropical Storm Arlene toward the south. On its anticipated track Tropical Storm Arlene will stay west of Florida. Arlene could move near the western end of Cuba by Saturday evening.

TD 01 Intensifies Into Rare April Tropical Storm Arlene

Tropical Depression 01 intensified into Tropical Storm Arlene on Thursday afternoon.  Tropical storms rarely form over the Atlantic Ocean in April and Arlene is only the second storm known to do so during the satellite era.  Of course, it would have been much harder to detect tropical storms like Arlene prior to the use of geostationary satellites for meteorological monitoring.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Arlene was located at latitude 37.7°N and longitude 42.0°W which put it about 815 miles (1315 km) west of the Azores.  Tropical Storm Arlene was moving toward the west-northwest at 25 m.p.h. (41 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 936 mb.

A circular ring of showers and thunderstorms developed around the center of circulation of Subtropical Depression 01.  Additional narrow rainbands organized around the core of the circulation and the convection assumed a more circularly symmetrical shape.  In addition data from satellites indicated that a weak warm core had formed at the top of the circulation.  A more circular shape and a warm core are characteristics of a tropical cyclone and the National Hurricane Center changed the classification of Subtropical Depression 01 to Tropical Depression 01 in the 11:00 a.m. EDT advisory on Thursday.  Showers and thunderstorms continued to develop around the center of circulation and Tropical Depression 01 was upgraded to Tropical Storm Arlene in the 5:00 p.m. EDT advisory on Thursday.

Tropical Storm Arlene is in an environment that would not normally be considered favorable for a purely tropical weather system.  It is moving over water where the Sea Surface Temperature (SST) is near 19°C.  However, an upper low just to the west of Arlene contains colder air.  Colder air in the upper levels is providing sufficient instability to generate showers and thunderstorms even though the SST is relatively cool.  The cooler SST does mean that the showers and thunderstorms are not as tall as they would be if the water was warmer.  The upper low west of the system is producing southerly winds which are blowing over the top of Tropical Storm Arlene.  However, since the thunderstorms are not as tall, some of the stronger upper level winds are blowing over the top of Arlene’s circulation and the vertical wind shear is not having as much of an effect as might be expected.

The environment is marginal for further intensification, but the circulation looks fairly intact at the current time.  The cool SST is limiting the amount of energy that the tropical depression can extract from the ocean.  However, since the vertical wind shear is not having as much of a negative impact on the depression, some intensification may be possible during the next 24 hours.  Eventually, the wind shear is forecast to increase and Tropical Storm Arlene is forecast to weaken.

Tropical Storm Arlene is caught in the circulation of a large low pressure system to its west.  Arlene is forecast to make a counterclockwise loop as it moves around the circulation of the larger low pressure system.  It is possible that the larger low could absorb the circulation of Tropical Storm Arlene.