Tag Archives: St. Denis

Tropical Cyclone Alvaro Starts Extratropical Transition

Tropical Cyclone Alvaro started to make a transition to an extratropical cyclone over the Southwest Indian Ocean south of La Reunion on Wednesday. At 10:00 p.m. EST on Wednesday the center of Tropical Cyclone Alvaro was located at latitude 26.8°S and longitude 54.9°E which put it about 405 miles (655 km) south of St. Denis, La Reunion. Alvaro was moving toward the southeast at 21 m.p.h. (33 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 998 mb.

Tropical Cyclone Alvaro began a transition to an extratropical cyclone on Wednesday. Alvaro moved over cooler water. In addition, an upper level ridge over the Southwest Indian Ocean produced strong westerly winds that blew toward the top of Alvaro’s circulation. Those winds caused strong vertical wind shear. The combination of cooler water and strong vertical wind shear caused the structure of Tropical Cyclone Alvaro to change. Thunderstorms were occurring in bands in the southeastern part of Alvaro’s circulation. Bands in the other parts of the circulation consisted primarily of showers and lower clouds. Winds to tropical storm force extended out 150 miles (240 km) from the center of Tropical Cyclone Alvaro.

Tropical Cyclone Alvaro will move through an environment unfavorable for a tropical cyclone during the next 24 hours. Alvaro will move over water where the Sea Surface Temperatures are colder than 26°C. It will continue to move under the southern part of an upper level ridge over the Southwest Indian Ocean. The upper level ridge will continue to cause strong vertical wind shear. The colder water and strong vertical wind shear will cause Tropical Cyclone Alvaro to continue its transition to an extratropical cyclone.

The upper level ridge over the Southwest Indian Ocean will steer Tropical Cyclone Alvaro toward the southeast during the next 24 hours. On its anticipated track, Tropical Cyclone Alvaro will pass south of Mauritius on Thursday.

Tropical Cyclone Dumako Passes North of La Reunion

Tropical Cyclone Dumako passed north of La Reunion on Monday morning. At 4:00 a.m. EST on Monday the center of Tropical Cyclone Dunako was located at latitude 16.6°S and longitude 54.6°E which put it about 275 miles (445 km) north of St. Denis, La Reunion. Dumako was moving toward the west-southwest at 18 m.p.h. (29 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h). The minimum surface pressure was 986 mb.

Small Tropical Cyclone Dumako passed north of Mauritius and La Reunion on Monday morning as it moved over the Southwest Indian Ocean. After Dumako intensified on Sunday, it appeared to be weakening on Monday morning. Drier air seemed to be causing thunderstorms to weaken. The strongest thunderstorms were occurring in a band in the eastern side of Dumako’s circulation. Bands in other parts of Tropical Cyclone Dumako consisted primarily of showers and lower clouds. The thunderstorms in the eastern side of Dumako were generating upper level divergence that pumped mass away from the tropical cyclone. Winds to tropical storm force extended out 70 miles (110 km) from the enter of circulation.

Tropical Cyclone Dumako will move through an environment that will be only marginally favorable for intensification during the next 24 hours. Dumako will move over water where the Sea Surface Temperatures are near 28˚C. It will move under the northern side of an upper level ridge over the Southwest Indian Ocean. The ridge will produce easterly winds that will blow toward the top of Tropical Cyclone Dumako. Those winds will cause moderate vertical wind shear. The wind shear will inhibit intensification. There is drier air to the north and west of Tropical Cyclone Dumako. The drier air could continue to inhibit the formation of thunderstorms around Dumako’s circulation. If drier air inhibits the formation of additional thunderstorms, then Tropical Cyclone Dumako is likely to weaken gradually during the next during the next 24 hours.

Tropical Cyclone Dumako will move north of a subtropical high pressure system over the Southwest Indian Ocean. The high pressure system will steer the tropical cyclone toward the west during the next 36 hours. On its anticipated track Tropical Cyclone Dumako 12S will reach the coast of northern Madagascar near Mananara in a little over 24 hours. Dumako is likely to be the equivalent of a tropical storm when it reaches northern Madagascar. Tropical Cyclone Dumako will bring gusty wins and locally heavy rain to northern Madagascar on Tuesday.

Tropical Cyclone Batsirai Passes North of La Reunion

The center of Tropical Cyclone Batsirai passed north of La Reunion on Wednesday night. At 10:00 p.m. EST on Wednesday the center of Tropical Cyclone Batsirai was located at latitude 19.1°S and longitude 55.4°E which put it about 100 miles (160 km) north of St. Denis, La Reunion. Batsirai was moving toward the west-southwest at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 130 m.p.h. (210 km/h) and there were wind gusts to 160 m.p.h. (260 km/h). The minimum surface pressure was 942 mb.

Tropical Cyclone Batsirai appeared to be in the midst of another eyewall replacement cycle on Wednesday night. The inner end of a rainband wrapped around the inner eye and eyewall. A second, larger eyewall surrounded the inner eyewall and the inner eyewall started to weaken. The outer eyewall contained a ring of strong thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Tropical Cyclone Batsirai. Storms near the core generated upper level divergence that mass away from the tropical cyclone.

Tropical Cyclone Batsirai continued to have a large circulation. Winds to hurricane/typhoon force extended out 60 miles (95 km) from the center of Batsirai. Winds to tropical storm force extended out 190 miles (305 km) from the center of circulation. The Hurricane Intensity Index (HII) for Tropical Cyclone Batsirai was 25.1. The Hurricane Size Index (HSI) was 21.3 and the Hurricane Wind Intensity Size Index (HWISI) was 46.6.

Tropical Cyclone Batsirai will move through an environment capable of supporting a strong tropical cyclone during the next 48 hours. Batsirai will move over water where the Sea Surface Temperatures are near 29˚C. It will move through a region where the upper level winds are weak and there will be little vertical wind shear. Tropical Cyclone Batsirai is likely to weaken during the next few hours while it completes the eyewall replacement cycle. Batsirai could strengthen again after it completes the eyewall replacement cycle.

Tropical Cyclone Batsirai will move north of a high pressure system over the South Indian Ocean. The high pressure system will steer Batsirai toward the west-southwest during the next several days. Tropical Cyclone Batsirai will bring gusty winds and locally heavy rain to La Reunion during the next 12 hours. Rainbands in the southeastern part of Batsirai’s circulation were also dropping heavy rain over Mauritius. The heaviest rain was falling on the eastern slopes of mountains where the winds were blowing up the slopes. Locally heavy rain could cause flash floods in some locations. Weather conditions on La Reunion and Mauritius will improve gradually when Batsirai moves farther away. On its anticipated track Tropical Cyclone Batsirai could approach the east coast of Madagascar south of Toamasina in 48 hours. Batsirai is likely to be the equivalent of a major hurricane when it reaches Madagascar.

Tropical Cyclone Diane Forms North of La Reunion

Tropical Cyclone Diane formed north of La Reunion on Friday.  At 10:00 a.m. EST on Friday the center of Tropical Cyclone Diane was located at latitude 19.3°S and longitude 56.2°E which put it about 110 miles (175 km) north-northeast of St. Denis, La Reunion.  Diane was moving toward the east-southeast at 18 m.p.h. (30 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 997 mb.

A distinct low level center of circulation developed in an area of low pressure east of Madagascar on Friday and the system was designated as Tropical Cyclone Diane.  The distribution of thunderstorms around Tropical Cyclone Diane was asymmetrical.  Many of the stronger thunderstorms were occurring northwest of the center of circulation.  Bands of showers and thunderstorms were developing east of the center of Diane.  Storms near the center of circulation were beginning to generate upper level divergence which was pumping mass away to the southeast of the tropical cyclone.

Tropical Cyclone Diane will move through an environment somewhat favorable for intensification during the next 24 to 36 hours.  Diane will move over water where the Sea Surface Temperature is near 28°C.  An upper level trough west of Madagascar and an upper level ridge east of Mauritius will interact to produce northwesterly winds which will blow toward the top of the tropical cyclone.  Those winds will cause moderate vertical wind shear which will inhibit intensification.  Tropical Cyclone Diane could intensify slowly during the next 24 to 36 hours.

The upper level trough and upper level ridge will steer Tropical Cyclone Diane toward the east-southeast during the next several days.  On its anticipated track Tropical Cyclone Diane could bring wind and rain to Mauritius within 12 hours.  Locally heavy rain could cause flash floods in some locations.