This case study combines examples of tropical cyclones that formed and travelled over the Pacific Ocean in 2021. We have tracked them using various satellite data and recorded some of the impacts they made in countries such as the Philippines and Mexico.
17 March 2023
10 March 2023
11-14 Oct, Mexico, USA
By Jochen Kerkmann
In 2021, while the busy Atlantic hurricane season caused several dangerous storms, tropical storms also formed in the eastern Pacific, including Hurricane Pamela, which made landfall in Mexico on 13 October.
The Category 1 hurricane came ashore northwest of the city of Mazatlán on Mexico’s west coast, downing trees, flooding streets and causing power outages.
On 7 October, the National Hurricane Center (NHC), in Miami, began monitoring a tropical wave centered over the southwestern Caribbean Sea for potential development in the Eastern Pacific. The wave crossed Nicaragua and Costa Rica, emerging over the Pacific the following day. The system strengthened into Tropical Storm Pamela at 21:00 UTC on 10 October. On 11 October, Pamela became a Category 1 hurricane, as the hurricane developed a large area of deep convection (but no eye).
This can be seen on Figure 1, which shows Hurricane Pamela on 12 October. Note the proximity of Hurricane Pamela and the deep upper-level trough over California. Figure 2 shows the landfall of Pamela and its decay over northern Mexico. The remnants of Pamela over Mexico, and the cold front of the mid-latitude cyclone (ex-Californian Low), would eventually start to interact, bringing strong rains to Texas and Oklahoma.
To better discriminate water from ice clouds within the frontal band over Texas on 13 October, Figure 3 shows an animation of the so-called Day Snow/Cloud Layers RGB product developed by CIRA. This product combines information from six different bands on the GOES ABI, to help distinguish water clouds from snow and ice clouds. Low water clouds are depicted in yellow, high ice clouds in pink/magenta. The algorithm uses combinations of reflective and infrared bands, that includes a cirrus mask from the 1.38μm channel (band 4), and a normalized difference snow index (NDSI). See the quick guide of the RGB product.
The moisture from ex-Pamela, and the approaching cold front from the mid-latitude cyclone over the central US, likely contributed to the development of a supercell storm over southern Texas on 14 October (Figure 4).
Unfortunately, no mesoscale sector (special GOES ABI 1-min scanning mode) was placed over Texas on that day; so Figure 5 shows the standard five-minute GeoColor RGB images of that storm. Note the long shadow of the cirrus anvil on the low-level clouds.
Note: according to the New York Times, eastern Pacific hurricanes rarely hit land. Similarly to Atlantic storm, the majority of Pacific storm systems track from east to west. This means that very few make any impact on land, i.e. they don’t really pose a threat to the US West Coast. The last time a hurricane struck California, according to the National Oceanic and Atmospheric Administration, was the San Diego hurricane of 1858, which brought winds of about 75mph.
14-21 April, Philippines, South China Sea
By Jochen Kerkmann, HansPeter Roesli, Ivan Smiljanic
Super Typhoon Surigae was the strongest ever early season typhoon in the North Pacific, when it formed in April 2021.
In late April Typhoon Surigae, known in the Philippines as Typhoon Bising, was a powerful tropical cyclone east of the Philippines. It became the strongest Northern Hemisphere tropical cyclone to form before the month of May, and one of the most intense tropical cyclones on record.
Surigae became annular on 19 April, following an eyewall replacement cycle, which created a very large eye that could still be clearly seen in a variety of satellite imagery (Figures 6 and 7).
Surigae strengthened at a pace that was double the rate needed to qualify for rapid intensification (jumping by more than 160km/h in a day and a half), and its 190mph peak winds were stronger than Hurricane Dorian, which ravaged the Bahamas at the start of September 2019. The threshold for Category 5 status is 156mph.
The Tropical Airmass RGB of 21 April (Figure 8) shows the extremely big eye (over 100km diameter), plus the presence of different airmasses at mid to high levels of the troposphere north and south of Surigae (the red v blue hues).
Figure 9 is zoomed in on different wave formations on top of the convective cloud bands surrounding Surigae’s eye. These wave formations are detected both in the visible and temperature signals of the AHI sensor. These are different types of gravity waves that are a consequence of very dynamic (vertical) processes associated to typhoon’s convection. Some of these waves are very untypical, like the quasi-stationary one stretching from the typhoon’s centre towards (roughly) Taiwan, annotated by the blue arrows in water vapour imagery (Figure 10).
Another sign of intense vertical motions are the radial cirrus bands that emerge from the system at the tropopause level. These are seen better in the looping water vapour (WV) imagery (Figure 10), appearing as outward facing linear structures, around the typhoon’s eye. These also appear far away from the Surigae’s eye, as red linear clouds over South China Sea.