Month: November 2019

Nov. 25, 2019 – NASA Tracking Extra-Tropical Storm Sebastien towards the U.K.

NASA’s Aqua satellite passed over eastern North Atlantic Ocean and captured an infrared view of what is now Extra-tropical cyclone Sebastien. Sebastien transitioned from a tropical storm to an extra-tropical storm on Nov. 24. It has coupled with a cold front and is now headed for the United Kingdom.

Sebastien’s Final Advisory

At 10 p.m. EST on Sunday, Nov. 24 (0300 UTC Nov. 25), NOAA’s National Hurricane Center (NHC) issued the final advisory on Sebastien. At that time, the center of Post-Tropical Cyclone Sebastien was located near latitude 41.0 degrees north and longitude 28.9 degrees west. It was centered 230 miles (370 km) north-northwest of the Azores Islands. Sebastien was moving toward the northeast near 40 mph (65 kph) and this motion is expected to continue for the next day or so. Maximum sustained winds are near 60 mph (95 kph) with higher gusts. Post-tropical cyclone Sebastien should maintain its intensity before merging with another low during the next day or two. The estimated minimum central pressure is 993 millibars. 

NHC’s Forecaster Latto noted “Sebastien has lost its tropical characteristics this evening. The deep convection has decoupled from the low-level circulation, and these features are now separated by a distance of 100 nautical miles and increasing. Two [satellite] passes revealed that the surface low is becoming stretched out, and there is some evidence of a boundary, possibly a front, extending northeast from the center. Furthermore, recent observations from the Azores indicated a slight temperature decrease as the center passed by to the north of those islands, suggesting that a weak cold front is associated with the cyclone. Based on all of these data, there is high confidence that Sebastien has transitioned to an extratropical cyclone.”

What does Extra-tropical Mean?

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.

NASA’s Infrared View of Sebastien

NASA’s Aqua satellite used infrared light to analyze the strength of storms in Sebastien. Infrared data provides temperature information, and the strongest thunderstorms that reach high into the atmosphere have the coldest cloud top temperatures. On Nov. 25 at 0400 UTC (Nov. 24 at 11 p.m. EST), Aqua passed over the storm after it had become associated with a cold front. The coldest cloud top temperatures were near minus 50 degrees Fahrenheit or minus 45.5 degrees Celsius. The infrared imagery revealed that the strongest precipitation had become elongated, resembling a frontal system.

Sebastien Headed to the U.K.

The United Kingdom Meteorological Service noted that rains from Sebastien are headed toward the U.K. by Tuesday. The storm is forecast to affect southern England and then move northeast. The Met Office warned that flood-ravaged areas may be affected by more heavy rain over the next several days. The U.K. Met Service issued several yellow weather warnings in southwest and northeast England as torrential showers are expected from Sebastien’s remnants. For updated forecasts, visit: https://www.metoffice.gov.uk/

Hurricanes are the most powerful weather event on Earth. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.

By Rob Gutro
NASA’s Goddard Space Flight Center

Nov. 22, 2019 – NASA’s Infrared Analysis of Tropical Storm Sebastien Sees Wind Shear

Tropical Storm Sebastian continued to move in a northeasterly direction through the North Atlantic Ocean as NASA’s Aqua satellite passed overhead. Infrared imagery from an instrument aboard Aqua revealed very high, powerful storms with very cold cloud top temperatures in the southwestern quadrant of the storm.  It also revealed that the storm was being sheared apart by outside winds.

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.

On Nov. 22 at 1:15 a.m. EST (0515 UTC), the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite used infrared light to analyze the strength of storms within the tropical cyclone. MODIS found those strongest storms only in the southwestern side of the storm where cloud top temperatures were as cold as or colder than 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.

The reason the strongest storms were happening only in that quadrant is that outside winds from the southwest are pushing the bulk of clouds and precipitation to the northeast. 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.

At 11 a.m. EST (1500 UTC), the center of Tropical Storm Sebastien was located near latitude 25.2 degrees north and longitude 55.3 degrees west about 695 miles (1,120 km) northeast of the Northern Leeward Islands.

Sebastien is moving toward the east-northeast near 15 mph (24 kph). An east-northeastward or northeastward motion at a similar forward speed is expected through the weekend of Nov. 23 and 24. Maximum sustained winds have decreased to near 50 mph (85 kph) with higher gusts.  The estimated minimum central pressure is 1,000 millibars.

The National Hurricane Center said that strong wind shear is expected to prevent Sebastien from getting better organized, so gradual weakening is anticipated. Sebastien is forecast to dissipate by early next week.

Hurricanes are the most powerful weather event on Earth. NASA researches these storms to determine how they rapidly intensify, develop and behave. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.

By Rob Gutro
NASA’s Goddard Space Flight Center

Nov. 21, 2019 – NASA Found Atlantic’s Sebastien Was Fighting Wind Shear

NASA’s Terra satellite captured a visible image of Tropical Storm Sebastien that showed wind shear had pushed the bulk of its clouds and showers to the southeast of the center.

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.

On Nov. 20, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Terra satellite provided a visible image of Tropical Storm Sebastien. The MODIS image showed the center of circulation appeared to be surrounded by wispy clouds, and that northwesterly wind shear had pushed the bulk of Sebastien’s clouds and showers southeast of the center. In addition, the low-level center of circulation was exposed to outside winds.

On Nov. 21, the National Hurricane Center Sebastien said that the storm continues to produce a large area of deep convection over the eastern semicircle of the circulation, but the banding features are not very well defined.

On Nov. 21 at 10 a.m. EST (1500 UTC), the center of Tropical Storm Sebastien was located near latitude 23.5 degrees north and longitude 60.5 degrees west about 405 miles (650 km) north-northeast of the Northern Leeward Islands.

Sebastien is moving toward the north-northeast near 8 mph (13 kph).  A faster northeastward motion is expected during the next few days. The estimated minimum central pressure is 999 millibars.

Maximum sustained winds are near 60 mph (95 kph) with higher gusts. Sebastien is forecast to become a hurricane by tonight, but a weakening trend is expected to begin by late Friday. The system is likely to become an extratropical cyclone by Saturday when it is forecast to become embedded in a frontal zone.

NASA’s Terra satellite is one in a fleet of NASA satellites that provide data for hurricane research.

Hurricanes and typhoons are the most powerful weather event on Earth. NASA’s expertise in space and scientific exploration contributes to essential services provided to the American people by other federal agencies, such as hurricane weather forecasting.

By Rob Gutro
NASA’s Goddard Space Flight Center