Current Snapshot

The Pacific Disaster Center’s (PDC Global) Friday, March 28, 2025, Tropical Cyclone Activity Report…for the Pacific Ocean, the Indian Ocean, and adjacent Seas

Current Tropical Cyclones:

Tropical Cyclone 27S (Courtney)…is located approximately 385 NM southwest of Cocos Islands

Tropical Cyclone 28S (Dianne)…is located approximately 137 NM northeast of Broome, Australia – Final Warning

Northeast Pacific Ocean: There are no Tropical Cyclones

The last regularly scheduled Tropical Cyclone Activity Report of the 2024 eastern North Pacific Hurricane Season has been issued. Routine issuance of this section of the PDC product will resume on May 15, 2025. During the off-season, Special Tropical Weather Outlooks will be issued as conditions warrant by the NHC.

Central Pacific Ocean: There are no Tropical Cyclones

The 2024 central North Pacific hurricane season has ended. As such, the final routine Tropical Cyclone Activity Report for the 2024 season has been issued. Routine issuance of this section of the PDC product will resume on June 1, 2025. During the off-season, Special Tropical Weather Outlooks will be issued as conditions warrant by the CPHC.

Western Pacific, Indian Ocean, and adjacent Seas: 

South Indian Ocean

Tropical Cyclone 27S (Courtney)

According to the JTWC warning number 13, sustained winds were 115 knots with gusts to near 140 knots

Tropical cyclone 27S (Courtney) has rapidly intensified over the past six hours, and animated enhanced infrared (eir) satellite imagery showing the system developing a pinhole eye feature. The eye began to emerge, reached its peak and in the subsequent hour has begun to cool and become a bit more ragged. However, color enhanced microwave imagery reveal beautifully symmetrical microwave eye feature, with a strong eyewall along the western half of the eye, but the eastern side is much weaker or even open in the ssmis image. Comparison with the 37ghz image shows a slight westward vortex tilt with height, due to mid-level moderate shear.

The environment remains favorable, with low deep-layer shear, warm ssts and good radial outflow aloft. Slightly higher mid-level shear is still a factor however, evidenced by the open eyewall on the upshear side of the vortex. The system will arc southwestward to south over the next 72 hours as it rounds the axis of the ridge which is shifting to a position southeast of TC 27S.

The system slows down after 72 hours as it begins to run into a low- to mid-level ridge firmly entrenched to the south. The system is likely to intensify a bit more over the next 12 hours or so, with the forecast calling for a peak of 115 knots by 12 hours then holding steady through 24 hours.

The system is quite compact and thus prone to rapid fluctuations in intensity, and rapid eyewall replacement cycles (erc), which could impact the intensity forecast. The current m-perc erc probability is less than 10 percent but likely to quickly ramp up due to the rapid intensification (ri). Regardless, the system has a bit more left in the tank but after 24 hours, shear will begin to increase sharply as a trough approaches from the southwest.

By 36 hours, shear begins to pick up, and sharply increases beyond 48 hours as the system moves south. The system will be sheared apart after 72 hours as shear increases to more than 40 knots, beginning a rapid weakening phase. Dry air begins to intrude from the north just after 72 hours and will completely engulf the vortex shortly thereafter, dooming TC 27S to slow demise.

Shortly after 72 hours, the system will begin to transition to a subtropical low (stt), however, it is forecast that it will be rapidly weakening at the same time and that it will dissipate prior to completing stt. As the system weakens below tropical storm strength, the remnant vortex will make a sharp turn westward, steered by the
southeasterly flow emanating from the strong ridge to the south.

Tropical Cyclone 28S (Dianne) – Final Warning

According to the JTWC warning number 4, sustained winds were 45 knots with gusts to near 55 knots

Animated enhanced infrared (eir) satellite imagery depicts cycling deep convection, lacking any distinct organization around the assessed center. The low level circulation center (llcc) is fully obscured by the convection and cirrus blowoff and the system lies on the extreme edge of the Broome radar coverage. However, a high resolution microwave image came in and saved the day, showing a relatively large llcc with cyclonically curved bands of strong convection wrapping into the low emissivity region (ler).

The environment remains favorable with low wind shear, very warm ssts and decent outflow aloft, though the short time remaining over water will be the primary factor in keeping a lid on the intensification of TC 28S.

Tropical cyclone 28S (Dianne) will continue tracking southward along the western side of the steering ridge through the entirety of the forecast period. Landfall is expected in the vicinity of Koolan Island within the next six hours or so. Continuing its trek southward, TC 28S may briefly pass back over the far southeastern portion of King Sound around 12 hours before moving further inland for the remainder of the forecast period.

The system could intensify a bit more in the few hours left over water as the ssts in this area are zesty, and shear is low. However, ingestion of dry air from the Australian landmass and disruption of the inflow layer due to terrain interaction mean that further intensification will be limited to just 5-10 knots.

Once the system is ashore it will start to weaken but the further west the track is, the longer it will maintain a relatively high intensity. But once it is firmly ashore to the southeast of Derby, TC 28S will rapidly weaken and dissipate between 24 and 36 hours.