By PDC’s Senior Weather
Specialist Glenn James
The Pacific Disaster Center’s (PDC Global) Tuesday, January 16, 2024, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas
Current Tropical Cyclones:
Tropical Cyclone 05S (Belal)…is located approximately 295 NM east-southeast of St Denis, La Reunion Island
Tropical Cyclone 06S (Anggrek)…is located approximately 315 NM northwest of the Cocos Islands
Northeast Pacific Ocean:
The North Pacific hurricane season officially ended on November 30, 2023. Routine issuance of the Tropical Weather Outlook will resume on May 15, 2024. During the off-season, Special Tropical Weather Outlooks will be issued as conditions warrant.
The eastern Pacific basin hurricane season was above normal, with 17 named storms, of which 10 were hurricanes and eight of those major hurricanes.
From August 16 to 21, Tropical Storm Hilary brought widespread heavy rainfall and flooding to Southern California, with some areas receiving up to 600% of their normal August rainfall. Hilary resulted in the first ever issuance of Tropical Storm Watches and Warnings for the Southern California coastline by NOAA’s National Hurricane Center. In addition, the Center distributed key hazard focused messages for Hilary in Spanish through the agency’s new language translation project.
Hurricane Otis made landfall near Acapulco, Mexico, on October 25 as a category-5 hurricane, with sustained winds of 165 mph. Otis holds the record as the strongest land falling hurricane in the eastern Pacific, after undergoing rapid intensification in which wind speeds increased by 115 mph in 24 hours.
Central North Pacific:
The central North Pacific hurricane season officially ended on November 30, 2023. Routine issuance of the Tropical Weather Outlook will resume on June 1, 2024. During the off-season, Special Tropical Weather Outlooks will be issued as conditions warrant.
The central Pacific basin had a near-normal season with four tropical systems traversing the basin.
Hurricane Dora, a category-4 storm, passed south of Hawaii in early August, marking the first major hurricane in the central Pacific basin since 2020. The strong gradient between a high pressure system to the north and Dora to the south was a contributing factor to the wind-driven, fast-moving wildfires in Hawaii.
Western Pacific, Indian Ocean and adjacent Seas:
South Indian Ocean…
Tropical Cyclone 05S (Belal)
According to the JTWC warning number 9, sustained winds are 50 knots…with gusts to near 65 knots.
Animated multi-spectral satellite imagery depicts tropical cyclone 05S (Belal) continuing to track towards the southwest. Elevated mid-level wind shear (20-25 knots) has steadily decoupled the storm over the last twelve hours, revealing an open low level circulation center (llcc) offset to the northwest from the upper-level convection.
Outflow aloft primarily flows southeast from the dislocated region of upper-level convection. Clear regions to the west of Belal wrap into the storm as dry air continues to engulf and weaken the system. Sea surface temperatures continue to support development.
TC 05S (Belal) is forecast to track east-southeast through 48 hours while steered by the ridge to the northwest. The system slows down significantly by 36 hours, as it runs into a building ridge to the east which effectively blocks further eastward progression. After 48 hours, Belal will veer sharply southwest as the ridge to the north weakens and the steering influence shifts to the low-to mid-level mid-latitude ridge to the south.
Belal is anticipated to maintain 50 knot intensity through 24 hours as competing environmental factors offset one another. By 24 hours however, the system will experience a more rapid weakening trend, as wind shear is anticipated to increase to approximately 30 knots by 48 hours and increase to 55-60 knots by 96 hours.
A radiosonde sounding shows dry air is expected to continue to entrain into the system and weaken the storms intensity as it travels to the east-southeast and then west-southwest. The combination of the dry air entrainment and the mid-level wind shear are anticipated to overcome the favorable sea surface temperatures and dissipate the storm by 72 hours.
Tropical Cyclone 06S (Anggrek)
According to the JTWC warning number 4, sustained winds are 45 knots…with gusts to near 55 knots.
Animated multi-spectral satellite imagery depicts tropical cyclone 06S (Anggrek) stagnating in a quasi-stationary position as it has had little forward momentum over the last 12 hours. Deep layer convection persists but is confined to the western semicircle due to the influence of persistent easterly shear vector.
Equatorward outflow aloft is evident with cirrus shielding expanding to the northwest. Despite low deep level shear, estimated at 5 knots, mid-level shear is approximately 25 knots based on GFS model soundings.
Environmental analysis reveals a favorable environment with low deep layer shear, with the noted higher mid-level shear, moderate poleward and equatorward outflow and warm sea surface temperatures. The system is to the south of the near equatorial ridge (ner), but north of a subtropical ridge (str), with a resulting weak steering environment.
While currently quasi-stationary, TC 06S will begin to move out slowly to the east-southeast shortly as the gradient with the ner strengthens, with track speeds expected to remain below 3 knots for the next 24 hours. By 48 hours, the ner will form a north-south ridge complex east of the system, extending from Borneo to the west of Learmonth, Australia, forcing TC 06S to travel south-southwest through 72 hours.
A competing steering environment sets up after 72 hours as the ner pushes south to near Singapore, while a str develops to the south of the TC, generating another weak steering pattern. This will cause the system to slow down to a crawl, or become quasi-stationary, through the remainder of the forecast period.
As the storm moves southward, it moves intoa slightly more favorable environment with the mid-level shear
decreasing slightly and improves upper-level outflow, which will
allow for a brief period of intensification through 36 hours. After 48 hours, the mid-level shear (20-25 knots), reduced outflow, and dry air
entrainment will choke the system, causing a slow but steady drop in intensity, with the system ultimately anticipated to dissipate by 120 hours.