Tag: tropical cyclone

Hurricane John Gives Southern Mexico a Surprise One-Two Punch

On Monday evening, Sept. 23, 2024, an unusual hurricane struck southern Mexico, dumping 20 inches of rainfall along the coast according to estimates from NASA’s IMERG precipitation product. The following image shows these rainfall estimates.

Hurricane John (2024) rainfall accumulation

Observations from an international constellation of satellites were the starting point for calculating these estimates, and the data confirm that forecasters in prior days were right to warn of possible heavy rainfall. Forecasters did have trouble predicting the storm’s track and intensity, though. In the rural area of southwestern Mexico where Hurricane John struck, there are few rain gauges that provide public data in real-time, so having calibrated multi-satellite near real-time precipitation estimates like IMERG available is particularly valuable for understanding this storm as it unfolded.

The contours in the image cover the areas where the IMERG algorithm estimated that 5 inches (blue) to 36 inches (bright red) of rainfall fell during a four-and-a-half-day period ending on Friday, Sept. 27, at 3 a.m. CST (0900 UTC). The dashed yellow line in the image shows the U.S. National Hurricane Center’s estimate of the path taken by the storm’s low-pressure center.

According to NOAA hurricane track data, approximately once a year during the past 50 years, one major hurricane over the eastern Pacific has passed within 800 miles of this part of southern Mexico. Almost all of these hurricanes moved roughly west over the ocean, parallel to the coast. Before Hurricane John this year, only two other times during the past 50 years has a major hurricane made landfall within 150 miles of where Hurricane John hit Mexico on Monday. On Sept. 23, John made landfall near the small, coastal village of Punta Maldonado, which is located about 100 miles east of the town of Acapulco. The two other hurricanes that had made landfall in the same region in prior years were Hurricane Pauline in 1997 and Hurricane Otis in 2023.

John was just a 40-knot tropical storm at 3 a.m. CST on Monday, and forecasters had only expected it to become a slightly stronger tropical storm during the following 24 hours before making landfall and dissipating. Instead, John experienced extremely rapid intensification to become a 105-knot Category 3 hurricane on the Saffir-Simpson scale. This intensification occurred during a period that was merely 18 hours long, immediately before landfall. Following landfall, societal impacts were moderated by the fact that the storm hit a low-population region of Mexico.

According to the National Hurricane Center, John made landfall around 9:15 p.m CST in Mexico on Monday evening (Sept. 23, 2024), which was 0315 UTC on Tuesday morning, Sept. 24, in universal time.

On Tuesday, Sept. 23, Hurricane John was forecast to dissipate over land, and for part of Tuesday, the National Hurricane Center stopped issuing advisories for it. However, the storm’s remnants moved over the Pacific Ocean again where the system regained hurricane strength (65-knot winds) by Thursday, Sept. 26. The next day, John weakened to tropical-storm strength before striking Mexico a second time at a location west of its first landfall earlier in the week.

For more information about the IMERG algorithm and the NASA Global Precipitation Measurement (GPM) mission that IMERG is part of, please visit the GPM website: https://gpm.nasa.gov. Credits: Image and caption by Owen Kelley.

References:

NOAA Historical Hurricane Tracks webpage, https://coast.noaa.gov/hurricanes.

NHC, Discussion #3, https://www.nhc.noaa.gov/archive/2024/ep10/ep102024.discus.003.shtml. Intensity was 40 kt at 3AM CST on Monday, Sept. 23, 2024. Intensity was forecast to increase 20 kt in the following 24 hours.

NHC, Discussion #7, https://www.nhc.noaa.gov/archive/2024/ep10/ep102024.discus.007.shtml. Intensity increased to 105 kt, making John category 3 as of 9PM CST Monday, Sept. 23. The intensity estimate was influence by passive-microwave satellite data (SSMIS) and by T-values from infrared geosynchronous satellite data.

NHC, Discussion #8, https://www.nhc.noaa.gov/archive/2024/ep10/ep102024.discus.008.shtml. Landfall time was 9:15PM CST Monday, Sept. 23, with 105-kt category-3 winds. This time is the same as 0315 UTC, Tuesday, Sept. 24, 2024.

NHC, rain potential images, posted on https://www.nhc.noaa.gov. These images were issued between Sept. 23, 2024, 1200 UTC and Sept. 25, 2024, 1530 UTC. These images showed a narrow area with 20-30 inches of 3-day rainfall accumulation along the coast of the Mexican states of Oaxaca or Guerrero.

Hurricane Debbie (2024) Stalls off the Coast of South Carolina

Hurricane Debby precipitation accumulation 12UTC 3 Aug to 0UTC 9 Aug 2024 — Hurricane Debby’s rainfall accumulation During August 3-9, 2024

Since 2014, NASA has run the IMERG multi-satellite algorithm to estimate how much precipitation falls over the globe every 30 minutes on a grid with 0.1-degree resolution in latitude and longitude. Each grid box is approximately a square seven miles to a side at the Equator.

Every few years, the team of scientists that develop the IMERG algorithm deliver a new version of the software. They give the algorithm code to the NASA Goddard Precipitation Processing System (PPS) to run. Analysts and computer programmers with George Mason University’s CEOSR assist with running the algorithm and detecting anomalies in its output. When a new version of IMERG is delivered, NASA goes back over 23 years of satellite observations to give updated precipitation estimates that cover every 30 minutes of that entire period.

In 2024, NASA released Version 7 of the IMERG algorithm. An example accumulation from this version of the algorithm is shown above, covering five and a half days of observations of Hurricane Debby. Debby impacted the United States East Coast in August 2024. For part of that time, Debby was stalled off the coast of South Carolina, which means that the hurricane brought on shore a great deal of moisture which fell as large rainfall accumulations.

CEOSR team members used ancillary datasets to help evaluate the quality of the IMERG precipitation accumulations of Hurricane Debbie. The red triangles are locations of preliminary tornado reports associated with Hurricane Debbie according to the NOAA Storm Prediction Center. The violet-colored bow ties are locations where the USGS measured major
flooding at a steam gauge, as reported by the NOAA Water Prediction System. The orange and red squares are locations where rain gauges measured accumulation in excess of 14 or 17 inches, respectively. These gauge data were published in a discussion by the NOAA Weather Prediction Center.

The image’s filled contours in the image show precipitation estimates from the near real-time run of Version 7 IMERG. These near real-time estimates are known as the Late IMERG run. Weather forecasting agencies, disaster management organizations, and researchers can download these estimates approximately 16 hours after the satellite observations were collected. The path taken by the low-pressure center of Hurricane Debby is show with the white dashed line as reported in real-time by the National Hurricane Center.

As can be seen in the image, the maximum accumulation reported by the rain gauges occurred mostly over South Carolina within 50 miles of the coast. Many of the tornadoes and flooding stream gauges were also located this close to the sea. In contrast, the near real-time accumulations from IMERG were largest further inland or off the coast.

Because IMERG relies heavily on satellite estimates, it does not always capture the fine-scale structure of precipitation from severe storms with sharp precipitation gradients. Over much of the world’s oceans and even parts of continents, ground-based precipitation estimates are sparse, so there is interest in improving the IMERG algorithm based on comparisons with ground data where plentiful, such as over much of the United States.

CEOSR researcher Owen Kelley examined Version 7 IMERG accumulations from other hurricane impacting the United States coast in prior years to see if the new Version 7 algorithm always has errors matching the spatial pattern seen here with Hurricane Debby (2024). He determined that the new algorithm does not habitually make this mistake. NASA and CEOSR researchers will continue to evaluate the new version of IMERG with the aim of helping NASA to release an improved version in approximately 2 years.

Hurricane Ian Crosses Florida and Heads Toward South Carolina

Hurricane Ian’s rainfall accumulation up to 5AM EDT on September 30, 2022

As Hurricane Ian impacts Florida and South Carolina, NASA IMERG algorithm provides estimates of Ian’s rainfall over both land and sea. CEOSR team members assist NASA with visualizing this data and with monitoring the performance of the IMERG algorithm. Such evaluations assist with improving the algorithm, a new version of which is due to be released later this year or in early 2023.

The image above shows the rainfall accumulation from Hurricane Ian from when it formed in the Caribbean on September 25, 2022, through when it approached the coast of South Carolina on September 30. On September 28 and 29, Ian cross Florida going west to east from Ft. Myers to Cape Canaveral.

The image also show the locations of tornadoes and river flooding in Florida that were associated with the passage of Hurricane Ian. There were preliminary reports of tornadoes over southern Florida the night before Ian’s Florida landfall, which are marked by red triangles in the image. The tornadoes were associated with a large, persistent band of heavy rain that maintained a position
to the east of Hurricane Ian’s inner core during the days prior to the Florida landfall.

On September 29, the day Ian left Florida, numerous USGS stream gauges reach major-flood stage, meaning significant economic damage was expected. These stream gauges are marked with purple
bows in the image. Florida’s inland flooding was caused by Ian’s heavy rainfall. Along the coast, storm surge contributed to the height of the flood water.

Lightning before Landfall

Prior to making landfall in Florida on September 28, Hurricane Ian intensified over the Gulf of Mexico. During this time, its inner core dropped a considerable amount of rain and also exhibited many lightning flashes. This period is show in the image below.

Hurricane Ian’s rainfall accumulation during its approach to landfall in Florida

In the Gulf of Mexico, Ian’s eyewall was seen to contain particularly vigorous storm cells. Lightning was observed in Ian’s eyewall, whereas lightning had been near absent from Ian’s eyewall prior Ian passing over Cuba. Lightning strokes from the World Wide Lightning Location Network (WWLLN) are displayed in the image as small yellow dots. Over the Gulf of Mexico, the period of active eyewall lightning can be identified using the white dots in the image that indicate six-hourly locations of Hurricane Ian’s low-pressure center, as estimated by the National Hurricane Center.

Once in the Gulf of Mexico, Hurricane Ian intensified and underwent an eyewall replacement cycle early on September 28, according to the National Hurricane Center. During this period, NASA’s IMERG algorithm estimates that the rainfall accumulation under Ian’s inner core reached 12 to 20 inches. This accumulation is much higher than the 5-to-12-inch accumulation that Ian’s inner core had produced the day before, when the storm was located south of Cuba.

On September 27, stretching for several hundred miles to the east of Hurricane Ian’s inner core was a band of heavy rain storms and thunderstorms. These storms are seen in the IMERG rainfall accumulation, covering the southern tip of Florida during this period. During the night of September 27 and morning of September 28, these storms spawned a number of tornadoes according to preliminary reports from NOAA. These tornadoes are displayed as red dots in the image.

Credits: WWLLN data from the University of Washington with support from Jeremy Thomas and Natalia Solorzano at DigiPen Insitute of Technology and NorthWest Research Associates. Visualization Owen Kelley (CEOSR/NASA).

Hurricane Fiona from Caribbean to Canada

Hurricane Fiona and Its Landfall in Canada — Hurricane Fiona and Its Rainfall in Canada

Rainfall In Nova Scotia, Canada

CEOSR team members tracked Hurricane Fiona as it approached Canada in September, 2022. One of the tools they used was NASA’s IMERG algorithm, which provides estimates of global rainfall rates every 30 minutes with 0.1 degree latitude-longitude resolution. IMERG estimates of Hurricane Fiona’s rain accumulations in Nova Scotia were similar but somewhat lower than rain-gauge accumulations for the event. IMERG’s rainfall estimates are only approximate because they rely on morphing satellite microwave observations and on more frequent but less direct estimates of rainfall based on satellite infrared observations. None the less, over the open ocean, IMERG’s precipitation estimates are among the best available because the ocean is none instrumented with rain gauges or ground radars.

At approximately 4 AM local time (Atlantic Daylight Time) on Saturday, Sept. 24, Hurricane Fiona made landfall in Canada with a surface pressure of only 931 hPa at its center according to the National Hurricane Center (NHC). By 6 AM that morning, the NASA IMERG algorithm estimated that Hurricane Fiona had dropped in excess of 6 inches of rainfall off the coast of Nova Scotia. Rain was still accumulating over Atlantic Canada at that time. The image below shows these IMERG rainfall estimates and the NHC estimate of the distance that tropical-storm strength winds (39 mph, 34 knots) extend from the hurricane’s center.

Fiona’s 3-day rainfall accumulations in Canada were generally in the 2-to-8-inch range, according to rain-gauge data provided by the Canadian government: historical data. Selected gauges are shown in the image using circles that are color-coded with the same color table as the IMERG data. The IMERG-estimated 3-day accumulation over Nova Scotia is, for the most part, in the same 2-to-8-inch range as the rain-gauge data.

On September 23, which was one day before the Canadian landfall, IMERG estimated higher rainfall totals of over 12 inches when Hurricane Fiona passed near Bermuda. The storm was moving forward more slowly at that time, which increased rainfall totals. Rainfall totals were even higher when Hurricane Fiona passed through the Caribbean, as described in the section below.

September 23, a north-south-oriented cold front moved east off the shore of New England and the US Mid-Atlantic region. Rain and thunderstorms associated with that cold front are seen in the IMERG rainfall image, specifically along the coast of Maine and Massachusetts. The blue contour indicates 2-to-4-inch accumulation from the cold front along the Maine coast.

Rainfall in the Caribbean

Hurricane Fiona (2022) in the Caribbean Sea

Between Sept. 16 and 19, 2022, Hurricane Fiona struck Guadeloupe, Puerto Rico, and the Dominican Republic. NASA estimated precipitation in the region in near real-time using data from an international constellation of satellites processed by the IMERG algorithm.

IMERG estimated that Fiona dropped 12 to 18 inches of rainfall over Guadeloupe and over the ocean just south of Puerto Rico. Media sources and the National Weather Service reported that heavy rainfall accumulation extended somewhat further north, exceeding 20 inches over part of southeastern and central Puerto Rico. Some locations with particularly high accumulation from the storm are indicated with white dots in the image.

IMERG’s strength is its global reach, including regions of land and ocean where ground-based weather radar data is unavailable. Where ground radar or rain gauges are present, they may do better at capturing small, intense rain cells and the local effects of mountainous terrain. These strengths and limitations are illustrated by IMERG’s ability to depict Fiona’s full swath of rain across the Atlantic and its underestimation in Puerto Rico.

The National Hurricane Center reported that tropical-storm strength winds extended out from the center of the storm at the distances indicated in the three wind figures shown in the image. At the first two times shown (September 15 and 17), Fiona was a tropical storm with maximum sustained surface winds 39-73 mph. By September 19, Fiona had strengthened to a category-2 hurricane (96-110 mph winds).

Credits: Visualization by Owen Kelley (CEOSR/NASA).