Mar. 08, 2019 – NASA Finds Wind Shear Adversely Affecting Haleh
Visible imagery from NASA’s Terra satellite revealed northerly wind shear affecting Tropical Cyclone Haleh and continuing to weaken the storm.
On March 9 the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA’s Terra satellite provided a visible image of Haleh in the Southern Indian Ocean. The image showed the northeastern quadrant surrounded by wispy clouds, while the bulk of clouds and showers were pushed south and southwest of the center of circulation. Haleh also had a thick band of thunderstorms wrapping into the southern quadrant from the southeast.
On March 9 at 10 a.m. EST (1500 UTC) the Joint Typhoon Warning Center or JTWC noted that Haleh’s maximum sustained winds dropped to near 40 knots (46 mph/74 kph). It was centered near 32.9 degrees south latitude and 65.5 degrees east longitude. That’s 852 nautical miles south-southeast of Port Louis, Mauritius. Haleh was moving north-northwest and is forecast to turn to the north-northeast.
JTWC has forecast Haleh to weaken below the threshold of a tropical cyclone on March 9.
Mar. 07, 2019 – Tropical Cyclone Haleh Weakening in NASA-NOAA Satellite Imagery
Tropical Cyclone Haleh continues to weaken while being battered by outside winds. NASA-NOAA’s Suomi NPP satellite passed over the Southern Indian Ocean and captured an image the elongated storm.
Wind shear and cooler waters continue to weaken Haleh is it moves on a southerly course. The storm has fallen below the hurricane threshold and is now a tropical storm. On March 7, the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi NPP satellite showed Haleh appeared elongated from the outside winds.
In general, wind shear is a measure of how the speed and direction of winds change with altitude. In order to understand how it affects a tropical cyclone or hurricane, think of a tropical cyclone as a vertical rotating cylinder. The different levels of rotating winds in the center of tropical cyclones need to be stacked on top each other for the storm to strengthen. If there are outside winds pushing against the cylinder near the top, it affects the balance of the entire cylinder and that’s what happens when vertical wind shear pushes against a storm. It pushes the center and weakens (or wobbles) the rotation of the entire cylinder (storm) and stretches the storm out.
The Joint Typhoon Warning Center or JTWC reported “animated multispectral satellite imagery depicts a 130 nautical-mile cirrus cloud [high clouds] shield [layer] with isolated deep convection [strong storms] that is obscuring the low level circulation center. Low level rain bands are visible beyond the cirrus shield in all quadrants.”
At 10 a.m. EDT (1500 UTC) on March 7, JTWC noted that the center of Tropical Cyclone Haleh was located near latitude 27.7 degrees north and longitude 67.0 degrees east. That’s about 691 miles northeast of Port Louis, Mauritius. Maximum sustained winds have decreased to 69 mph (60 knots/111 kph).
The storm is forecast to become extra-tropical by March 8. When a storm becomes extra-tropical, it means that a tropical cyclone has lost its “tropical” characteristics. NOAA’s National Hurricane Center defines “extra-tropical” as a transition that implies both poleward displacement (meaning it moves toward the north or south pole) of the cyclone and the conversion of the cyclone’s primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force.
Mar. 06, 2019 – NASA Sees Tropical Cyclone Haleh Weakening
Tropical Cyclone Haleh continued to move in a southerly direction in the Southern Indian Ocean when NASA-NOAA’s Suomi NPP satellite passed overhead.
Suomi NPP passed over Haleh on March 6 and the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument provided a visible image of the storm. The VIIRS image showed a large area of thunderstorms wrapping into the center and the storm appeared to be elongating toward the southeast. The elongation of the storm is a result of outside winds, or moderate to strong vertical wind shear, and is indicative of weakening.
On March 6 at 10 a.m. EDT (1500 UTC) Haleh was located at 23.9 degrees south and 68.7 degrees east. That’s about 690 nautical miles east-southeast of Port Louis, Mauritius, has tracked southwestward. Maximum sustained winds had decreased to 75 knots (86 mph/139 kph).
Haleh is forecast to transition into an extra-tropical storm in two days and continue weakening.
Mar. 05, 2019 – NASA’s Infrared Vision Reveals Tropical Cyclone Haleh’s Power
Tropical Cyclone Haleh maintained an eye as NASA’s Aqua satellite passed overhead and collected temperature information on the storm and the ocean waters it was moving through.
Haleh developed as a tropical storm in the Southern Indian Ocean on March 2, about 337 nautical miles south-southeast of Diego Garcia. Haleh continued to intensify as it moved in a southerly direction and reached hurricane-force on March 3.
The Atmospheric Infrared Sounder or AIRS instrument aboard NASA’s Aqua satellite passed over Tropical Storm Cyclone Haleh on March 4 at 4:11 a.m. EDT (0911 UTC) and analyzed the storm in infrared light. Infrared light provides temperature data and that’s important when trying to understand how strong storms can be. The higher the cloud tops, the colder and the stronger they are.
When Aqua passed over Haleh, the AIRS instrument found coldest cloud top temperatures in thunderstorms around the eye of the storm, where temperatures were as cold as minus 63 degrees Fahrenheit (minus 53 degrees Celsius). Storms with cloud top temperatures that cold have the capability to produce heavy rainfall.
At 11 a.m. EDT (1500 UTC) on March, 5, 2019, the Joint Typhoon Warning Center or JTWC noted the center of Tropical Cyclone Haleh was located near 21.1 degrees south latitude and 71.7 degrees east longitude. That’s 920 miles east of St Denis, La Reunion Island. Haleh was moving toward the southwest. Maximum sustained winds are near 109 mph (95 knots/176 kph) with higher gusts. Some weakening is forecast to continue and the storm is expected to become extra-tropical in 5 days.