Tag Archives: CP06

Shear Hits Tropical Storm Niala and It Turns West

After intensifying earlier on Saturday, vertical wind shear began to affect Tropical Storm Niala and it turned westward.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Niala was located near latitude 16.9°N and longitude 152.8°W which put it about 245 miles (395 km) southeast of Hilo, Hawaii.  Niala was moving toward the west at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 992 mb.  A Tropical Storm Watch remains in effect for Hawaii County.

A large upper level trough centered northeast of Hawaii is causing southwesterly winds that are blowing over Tropical Storm Niala.  The wind shear is blowing the tops off the thunderstorms that try to form near the center of circulation.  As a result the low level circulation is exposed on satellite imagery.  The effect of the wind shear will be to weaken Niala even though it is over warm Sea Surface Temperatures.

Since there are not tall thunderstorms near the center of circulation, it is being steered toward the west by winds lower in the atmosphere.  A general westerly motion is expected for the next several days and Tropical Storm Niala is likely to pass south of Hawaii.

Niala Prompts Tropical Storm Watch for Hawaii

Tropical Storm Niala organized quickly southeast of Hawaii on Friday and the Central Pacific Hurricane Center issued a Tropical Storm Watch for Hawaii County.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Niala was located at latitude 15.7°N and longitude 150.4°W which put it about 415 miles (665 km) southeast of Hilo, Hawaii.  Niala was moving toward the northwest at 7 m.p.h. (11km/h).   The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1001 mb.

The circulation inside Niala consolidated quickly around the core of the tropical storm on Friday.  A primary rainband wrapped around the eastern and northern side of the circulation creating a small eyelike feature at the center of circulation.  At least three additional rainbands formed in the eastern half of the tropical storm.  There are fewer thunderstorms in the western half of the circulation which could indicated the presence of drier, more stable air in that part of Niala.

Niala is over water where the Sea Surface Temperatures are nearly 29°C.  The upper level winds are not too strong and the thunderstorms around the core of the circulation are generating upper level divergence,  Niala could strenthen during the next day or so.  A large upper level trough extends from northeast of Hawaii to the islands.  As Niala moves toward the northwest, it will start to move under strong southwesterly winds on the eastern side of the trough.  Those winds will create strong vertical wind shear and Niala will weaken as it approaches Hawaii.

A subtropical ridge is steering Niala toward the northwest and that general motion is expected to continue for another 24 hours.  When the wind shear weakens Niala, the circulation will not extend as high into the atmosphere.  After that time the winds lower in the atmosphere will steer the weakening Niala toward the west.