Mar. 20, 2020 – NASA Finds Herold a Fading Ex-Tropical Cyclone
Former Tropical Cyclone Herold is now a fading area of low-pressure in the Southern Indian Ocean and NASA’s Aqua satellite provided forecasters with a visible image.
On Mar. 20, 2020, the MODIS instrument that flies aboard NASA’s Aqua satellite provided a visible image ex-tropical cyclone Herold in the Southern Indian Ocean. Credit: NASA Worldview
On Mar. 19 at 4 p.m. EDT (2100 UTC), the Joint Typhoon Warning Center issued their final bulletin on Herold. At that time, Herold’s center was located near latitude 26.6 degrees south and longitude 73.0 degrees east, approximately 948 nautical miles east-southeast of Port Louis, Mauritius. Herold’s maximum sustained winds at the time were near 30 knots (34.5 mph/55.5 kph) making it a tropical depression. It has since weakened.
On Mar. 20, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite provided a visible image of the clouds circling Herold’s center. The clouds appeared wispy and devoid of heavy rainfall. The storm showed no strong convection (rising air that forms the thunderstorms that make up a tropical cyclone). Herold has moved over cooler waters which have sapped thunderstorm development.
Herold is expected to dissipate later in the day on Mar. 20.
NASA’s Aqua satellite is one in a fleet of NASA satellites that provide data for hurricane research.
Tropical cyclones/hurricanes are the most powerful weather events 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.
Mar. 19, 2020 – NASA Finds Little Strength Left in Tropical Cyclone Herold
Wind shear pushed former Tropical Cyclone Herold apart and infrared imagery from NASA’s Aqua satellite showed the system with very little strength remaining.
On March 19, 2020, the MODIS instrument that flies aboard NASA’s Aqua satellite gathered infrared data on Herold. MODIS showed minimal associated strong convection (rising air that forms the thunderstorms that make up tropical cyclones). Strongest thunderstorms had cloud top temperatures (blue) as cold as minus 50 degrees Fahrenheit (minus 45.5 Celsius). Credit: NASA/NRL
NASA’s Aqua satellite uses infrared light to analyze the strength of storms by providing temperature information about the system’s clouds. The strongest thunderstorms that reach high into the atmosphere have the coldest cloud top temperatures.
On March 19, 2020, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite gathered infrared data on Herold. Animated multispectral satellite imagery showed Herold’s low-level circulation center is partially exposed and there is minimal associated strong convection (rising air that forms the thunderstorms that make up tropical cyclones). Strongest thunderstorms had cloud top temperatures as cold as minus 50 degrees Fahrenheit (minus 45.5 Celsius).
At 5 a.m. EDT (0900 UTC), the center of Tropical Storm Herold was located near latitude 25.4 degrees south and longitude 71.1 degrees east, about 827 nautical miles east-southeast of Port Louis, Mauritius. Maximum sustained winds were near 46 mph (40 knots/74 kph).
Vertical wind shear, that is winds outside of a tropical cyclone at different heights in the atmosphere (the troposphere), push against a tropical cyclone and tear it apart. Herold is in an area of high wind shear blowing between 25 to 30 knots (29 to 35 mph/46 to 56 kph)
The Joint Typhoon Warning Center (JTWC) forecast notes that Herold will continue moving southeast and weaken rapidly because it is moving into an area of increased vertical wind shear speeds and cooler sea surface temperatures. The storm will dissipate within 24 hours.
Tropical cyclones/hurricanes are the most powerful weather events 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.
Mar. 18, 2020 – NASA Analyzes Tropical Cyclone Herold’s Water Vapor Concentration
When NASA’s Aqua satellite passed over the Southern Indian Ocean on Mar. 18, it gathered water vapor data that showed wind shear was adversely affecting Tropical Cyclone Herold.
On Mar. 18 at 5:40 a.m. EDT (0940 UTC), NASA’s Aqua satellite passed over Tropical Cyclone Herold, located in the Southern Indian Ocean. Aqua found highest concentrations of water vapor (brown) and coldest cloud top temperatures were south of the center. Credits: NASA/NRL
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. Strong wind shear from the northwest is battering Herold and pushing the strongest storms away from the center of circulation. Northwesterly winds affecting the storm are estimated between 25 and 30 knots (29 to 35 mph /46 to 56 kph)
What Water Vapor Reveals
NASA’s Aqua satellite passed over Tropical Cyclone Herold on Mar. 18 at 5:40 a.m. EDT (0940 UTC) and the Moderate Resolution Imaging Spectroradiometer or MODIS instrument gathered water vapor content and temperature information. The MODIS data showed highest concentrations of water vapor and coldest cloud top temperatures were pushed about 48 nautical miles southeast of the center of circulation.
MODIS data showed coldest cloud top temperatures were as cold as or colder than minus 70 degrees Fahrenheit (minus 56.6 degrees Celsius) in those storms. Storms with cloud top temperatures that cold have the capability to produce heavy rainfall.
Water vapor analysis of tropical cyclones tells forecasters how much potential a storm has to develop. Water vapor releases latent heat as it condenses into liquid. That liquid becomes the clouds and thunderstorms that make up a tropical cyclone. Temperature is important when trying to understand how strong storms can be. The higher the cloud tops, the colder and the stronger the storms.
Herold’s Status
On Wednesday, March 18, 2020 at 5 a.m. EDT (0900 UTC), the Joint Typhoon Warning Center or JTWC noted that Herold’s maximum sustained winds had dropped significantly since the previous 24 hours and the storm weakened from hurricane-force to tropical storm force. Maximum sustained winds were near 55 knots. Herold was centered near latitude 22.7 degrees south and longitude 66.1 degrees east, about 516 nautical miles east-southeast of Port Louis, Mauritius. Herold was moving to the southeast.
JTWC forecasters expect Herold to continue moving southeast and further away from land areas while continuing to weaken. Forecasters noted that the storm is becoming subtropical but could dissipate within a day or two before it completes that transition.
What is a Sub-tropical Storm?
According to the National Oceanic and Atmospheric Administration, a sub-tropical storm is a low-pressure system that is not associated with a frontal system and has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center.
Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources (atmospheric pressure), and are generally cold-core in the upper troposphere, often being associated with an upper-level low-pressure area or an elongated area or trough of low pressure.
NASA’s Aqua satellite is one in a fleet of NASA satellites that provide data for hurricane research.
Tropical cyclones/hurricanes are the most powerful weather events 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.
Mar. 17, 2020 – Tropical Cyclone Herold’s Eye Opens Further on NASA Satellite Imagery
As Tropical Cyclone Herold intensified, its eye appeared more defined in imagery taken by NASA’s Terra satellite.
On March 17, the MODIS instrument that flies aboard NASA’s Terra satellite took this image of Tropical Cyclone Herold and showed a well-developed hurricane which is maintaining a clearer eye. Credit: NASA Worldview
A Tropical Cyclone Warning class 3 was in force for Rodrigues Island on March 17. Rodrigues is an autonomous outer island of the Republic of Mauritius in the Southern Indian Ocean. It is about 42 square miles (108 square kilometers). Rodrigues Island is located about 350 miles (560 kilometers) east of Mauritius.
On March 17 at 5 a.m. EDT (0900 UTC), forecasters at the Joint Typhoon Warning Center (JTWC) noted “Infrared satellite imagery indicates a sharp intensification trend over the past 12 hours as the system formed an irregular 13-nautical mile wide eye.”
The Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Terra satellite confirmed that intensification. MODIS provided forecasters with a visible image of Tropical Cyclone Herold that revealed a much clearer eye than on March 16. The eye was no longer obscured by high clouds, and the Terra view was able to see down to the ocean’s surface through the eye. Powerful bands of thunderstorms circled the eye.
At 5 a.m. EDT (0900 UTC) on March 17, the center of Tropical Cyclone Herold was located near latitude 19.1 degrees south and longitude 60.4 degrees east, about 185 nautical miles east-southeast of Port Louis, Mauritius. Maximum sustained winds had increased to 100 knots (115 mph/185 kph).
The JTWC noted that Herold is moving southeast and is at peak intensity, while it is passing just west of Rodrigues. The storm is now expected to begin weakening before it becomes subtropical.
Tropical cyclones/hurricanes are the most powerful weather events 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.
Mar. 16, 2020 – NASA Sees Tropical Cyclone Herold’s Eye
NASA’s Aqua satellite passed over the Southern Indian Ocean and captured an image of a well-developed Tropical Cyclone Herold at hurricane strength, east of Madagascar.
On March 16, the MODIS instrument that flies aboard NASA’s Aqua satellite took this image of Tropical Cyclone Herold and showed a well-developed hurricane with a visible eye. Credit: NASA Worldview
Herold formed on March 13 as Tropical Cyclone 22S and once it intensified into a tropical storm, it was renamed Herold. Herold continued to strengthen and is now at hurricane-force.
On March 16, the Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA’s Aqua satellite provided forecasters with a visible image of Tropical Cyclone Herold and showed a well-developed hurricane with a visible eye, although slightly obscured by high clouds. Powerful bands of thunderstorms circled the eye.
At 5 a.m. EDT (0900 UTC) on March 16, the center of Tropical Cyclone Herold was located near latitude 15.7 degrees south and longitude 54.2 degrees east, about 295 nautical miles north-northwest of St. Denis, La Reunion Island. Maximum sustained winds were near 80 knots (92 mph/148 kph).
The Joint Typhoon Warning Center or JTWC noted that Herold is forecast to turn to the southeast, passing just west of Rodrigues. The storm will strengthen to 90 knots (104 mph/167 kph) later today before becoming subtropical.
Tropical cyclones/hurricanes are the most powerful weather events 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.
