Tag: TD6 2019

Aug. 29, 2019 – NASA Sees a Transitioned, Merging Extra-Tropical Storm Erin Off U.S. East Coast

Former tropical depression Erin has made the transition into an extra-tropical system off the eastern coast of the U.S. Infrared imagery from NASA’s Aqua satellite provided temperature data on storms associated with Erin and the weather system it is merging with.

NOAA’s National Hurricane Center or NHC issued the final advisory on Erin on Aug. 29 at 5 a.m. EDT.

On Aug. 29 at 2:30 a.m. EDT (630 UTC), the Moderate Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite used infrared light and found strongest thunderstorms associated with Erin where confined to a small area around the center. There, cloud top temperatures were as cold as minus 50 degrees Fahrenheit (minus 45.5 degrees Celsius). Infrared data provides temperature information, and the strongest thunderstorms that reach high into the atmosphere have the coldest cloud top temperatures.

Storms with colder cloud top temperatures were located far to the north of Erin’s center and are associated with the frontal system of which Erin is merging. Those storms had cloud top temperatures as cold as minus 70 degrees Fahrenheit (minus 56.6 Celsius). Cloud top temperatures that cold indicate strong storms with the potential to generate heavy rainfall.

Satellite imagery and scatterometer (wind) data indicate that Erin is merging with a frontal system and is now an extratropical low pressure area. On Aug. 30, Erin is expected to be absorbed by a larger extratropical low pressure area over eastern Canada.

When a storm becomes extra-tropical, it means that a tropical cyclone has lost its “tropical” characteristics. The 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.

At 5 a.m. EDT (0900 UTC), NHC noted that the center of Post-Tropical Cyclone Erin was located near latitude 36.1 degrees north and longitude 71.6 degrees west. That puts the center of Erin about 225 miles (365 km) east-northeast of Cape Hatteras, North Carolina.  The post-tropical cyclone is moving toward the north-northeast near 15 mph (24 kph). A turn toward the northeast and a faster forward motion are expected later today, with this motion continuing through Friday. Maximum sustained winds are near 35 mph (55 kph) with higher gusts.

The post-tropical cyclone is expected to strengthen a little on Friday, Aug. 30, before it is absorbed by a larger extratropical low over eastern Canada Friday night.

Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service online at: http://ocean.weather.gov/shtml/NFDHSFAT1.php.

By Rob Gutro
NASA’s Goddard Space Flight Center

Aug. 28, 2019 – NASA Finds Wind Shear Affecting Tropical Depression Erin

Visible and infrared imagery from NASA’s Terra satellite revealed that strong wind shear was adversely affecting Tropical Depression Erin, located about 200 miles off the Carolina coast.

On Aug. 27, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA’s Terra satellite provided a visible image of Tropical Depression Erin. In the image, Erin appeared as a swirl of clouds around its center with most of its clouds and thunderstorms pushed southeast of center. Strong northwesterly vertical wind shear was pushing at the storm.

Despite fighting wind shear on Aug. 27, Tropical Depression 6 strengthened into a tropical storm by 11 p.m. EDT, and was renamed Erin.

Infrared imagery from NASA’s Aqua satellite confirmed that wind shear was still affecting Tropical Storm Erin on Wednesday, August 28 at 3:25 a.m. EDT (0725 UTC). Infrared imagery reveals temperature data, and showed the only strong storms in the tropical storm were being pushed to the southeast. Strongest storms were as cold as minus 70 degrees Fahrenheit (minus 56.6 degrees Celsius).

In general, wind shear is a measure of how the speed and direction of winds change with altitude. Tropical cyclones are like rotating cylinders of winds. Each level needs to be stacked on top each other vertically in order for the storm to maintain strength or intensify. Wind shear occurs when winds at different levels of the atmosphere push against the rotating cylinder of winds, weakening the rotation by pushing it apart at different levels.

By 11 a.m. EDT (1500 UTC), Tropical Storm Erin had weakened back to a depression. At that time, the center of Tropical Depression Erin was located near latitude 33.6 degrees north and longitude 72.8 degrees west. That places the center of Erin about 190 miles (305 km) southeast of Cape Hatteras, North Carolina. The bulk of clouds and precipitation, however, are south of the center. However, because Erin is so far from the coast, there are no coastal watches or warnings in effect.

The depression is moving toward the north-northwest near 13 mph (20 kph). Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. The estimated minimum central pressure is 1006 millibars.

The cyclone is expected to turn northward later today and then north-northeastward early Thursday morning with an increase in forward speed.

NHC forecaster Daniel Brown noted in the Aug. 28 discussion, “The northwesterly shear that has been affecting Erin is forecast to decrease somewhat later today and tonight, but given the current structure of the system, little overall change in intensity is anticipated during that time. If convection does not re-develop closer to the center later today, Erin could become post-tropical.”

For updated forecasts, visit: www.nhc.noaa.gov

By Rob Gutro
NASA’s Goddard Space Flight Center

Aug. 27, 2019 – NASA Finds Tropical Depression Battling Wind Shear off the Carolina Coast

Newly formed Tropical Depression 6 in the Atlantic Ocean may have just formed, but it did so under adverse atmospheric conditions. The depression is battling wind shear and it’s apparent on imagery from NASA’s Aqua satellite.

Wind shear is a measure of how the speed and direction of winds change with altitude. When outside winds batter a tropical cyclone, it affects its circulation. A less circular storm tends to slow down in its spin and weaken.

Tropical Depression 6 or TD6 formed around 5 p.m. EDT on August 26 and has since been moving slowly while remaining a few hundred miles off the coast of the Carolinas.

On August 27 at 2:40 a.m. EDT (0640 UTC), the Moderate Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite used infrared light to analyze the strength of storms within the depression. Tropical cyclones are made of up hundreds of thunderstorms, and infrared data can show where the strongest storms are located. They can do that because infrared data provides temperature information, and the strongest thunderstorms that reach highest into the atmosphere have the coldest cloud top temperatures.

MODIS found those strongest storms had cloud top temperatures as cold as minus 80 degrees Fahrenheit (minus 62.2 Celsius). NASA research has found that cloud top temperatures that cold indicate strong storms with the potential to generate heavy rainfall. Those strongest storms were in a small area around the center of circulation. Less strong storms were pushed to the south by northerly wind shear.

The NHC or National Hurricane Center noted in their Discussion on Aug. 27 at 11 a.m. EDT “The depression, however, continues to be sheared with the low-level center to the north of the convection. The northwesterly shear currently affecting the depression is expected to continue, and only a small increase in intensity is anticipated in the next couple of days.”

NHC noted at 11 a.m. EDT (1500 UTC), the center of Tropical Depression Six was located near latitude 31.2 degrees north and longitude 71.2 degrees west. That’s about 385 miles (615 km) west of Bermuda and about 370 miles (600 km) southeast of Cape Hatteras, North Carolina.

The depression has been drifting northward near 2 mph (4 kph), and little motion is anticipated today. Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Some strengthening is expected, and the cyclone is forecast to become a tropical storm later tonight or on Wednesday.

NHC forecasters expect TD6 should begin to move generally northward and then northeastward on Wednesday over the open Atlantic.

For updated forecasts, visit: https://www.nhc.noaa.gov

By Rob Gutro
NASA’s Goddard Space Flight Center