Watching the Southern Hemisphere the Next 2 Weeks
I'd like to start off by wishing everyone at WU a happy New Year! As we reach the heart of the offseason in the Atlantic, we are also reaching the peak of cyclone season in the Southern Hemisphere, and right on cue the South Indian basin and South Pacific basin have heated up and look to continue producing cyclones in the next couple weeks. There are currently two active cyclones being warned on by the Joint Typhoon Warning Center. The first is Cyclone Freda in the South Pacific, currently located about 285 nautical miles NW of Noumea, New Caledonia, and moving SE at about 4 kts according to the JTWC. Freda was a powerful, well organized cyclone a few days ago, but is only a shell of its former self, as strong vertical wind shear has caused the low level center of the storm to become exposed, west of the deep convection. The JTWC currently estimates the maximum 1 minute sustained winds at 45kts. Wind shear is expected to remain high for the next few days, and the system should continue to weaken as it tracks S/SE. There are a couple possibilities as to what happens to the system beyond 3 or 4 days. One is that the strong wind shear and decreasing sea surface temperatures will simply cause the already weakened system to dissipate. However, by 4-5 days, a building ridge will cause Freda, or whatever remains of it, to turn sharply west. This will lead to a large decrease in wind shear, and with marginally favorable sea surface temperatures, there is a possibility that the system actually strengthens as it moves towards east Australia. This scenario is being portrayed by the GFS, particularly last night's 0z run, which took Freda into eastern Australia as a hurricane equivalent in about 6 days! The 6z run also brought the system towards the coast, but stalled it offshore before eventually bringing it in as a weak storm in about 9 days. The Euro, meanwhile, projects that the system will survive but simply meander for the next week, and by 180 hours the 0z Euro has it in almost the same exact spot its in right now! Clearly there is significant uncertainty in the forecast, and I would not expect that to change in the next couple days. The official JTWC forecast maintains Freda as a shallow warm core system for the next 5 days, and projects a sharp west turn in 4 days or so, followed by slight strengthening. Personally, I have a hard time believing much will be left of Freda in 4-5 days, but we will see.
Figure 1: Official JTWC forecast track of Freda.
Figure 2: Cyclone Freda. While most of the deep convection is impacting New Caledonia, the center of the storm is actually further west, away from the convection, an obvious sign of strong wind shear.
Cyclone Dumile Forms, but Struggling to Strengthen
Meanwhile, in the South Indian basin, the JTWC is currently issuing warnings on Cyclone Dumille, currently located about 550 nautical miles N of La Reunion island, moving SW at 8 kts. Dumile's maximum 1 minute sustained winds are estimated at 45 kts based off of a variety of Dvorak estimates. Both the GFS and ECMWF continue to forecast significant intensification of Dumile in the next three days as it is in a very favorable environment. So far, however, moderate wind shear has prevented significant strengthening as the center has been kept S/SE of the deep convection. Accordingly, the official peak intensity from JTWC was adjusted down to 100 kts from 110 kts in the latest warning. Peak intensity should occur in about three days, so Dumile does not have much time to strengthen. On satellite, the system does appear to be slowly getting more organized, so I think a 100 kt peak intensity is realistic if it develops an organized inner core by the end of today, which it has yet to do so far. After three days, Dumile will move into an environment of increasing shear and cooler waters, which will weaken the system and likely cause extratropical transition to begin within 6 days. Regarding short term track, Dumile is expected to move SSW, then turn more S and SSE by day 3, basically paralleling the coast of Madagascar. It is under the influence of a weakening ridge to its SE that has been causing its SW movement. As the ridge weakens further it will cause Dumile to turn more S and SE with time. Impacts on Madagascar should be minimal, but the bigger threat is on La Reunion island. Dumile is expected to pass just west of the island as a strengthening Category 2 or 3 cyclone in a little over 2 days. Anyone there should be prepared for deteriorating conditions within 48 hours.
Figure 3: Official JTWC forecast for Dumile.
Figure 4: Recent microwave pass of Dumile, showing no evidence of an organizing core.
Watching for More Development
Another area of low pressure is organizing in the NE part of the South Indian basin. Both the GFS and ECMWF forecast this system to develop in the next couple days and begin a long trek SW across the basin. It is too early to tell if this will affect land. Meanwhile, the GFS model is predicting the possibility of multiple Southern Hemisphere systems developing in the next several days. One potential area to watch will be off the NW coast of Madagascar/NE coast of Mozambique in 5-6 days. The GFS predicts a low forming there, and the 0z run last night brought it into NE Mozambique in about a week as a very weak system. However, it quickly moved the system back offshore, and showed strengthening in the Mozambique channel before another Mozambique landfall in 10-11 days. Then, it once again brings the system off the coast shortly after landfall, moves it south through the Mozambique channel, and by the end of the run, 384 hours out, the system appears poised to hit SE Mozambique as a very strong cyclone. The 6z run, meanwhile, showed the same system making landfall in NE Mozambique in about 8 days as a fairly well organized storm. It then skirts the coast just inland as it moves south for a couple days, but never manages to reemerge over water. The ECWMF does not show this system at all. Once again, time will tell. The 6z GFS developed a system off the NE coast of Madagascar in about a week as the previously described system neared landfall. It showed this storm meandering as a weak system in that area until about 10 days, when it began to strengthen. By 300 hours the storm began moving south, and the GFS blew it up into a complete monster by 312 hours to the end of the run, keeping it just offshore of Madagascar. Finally, the GFS shows a system forming around southern Indonesia in 5-6 days. The 0z run strengthened it slightly and moved it into northern Australia in about 8 days, while the 6z run showed a more SW track and brought it into NW Australia in about 10 days. Certainly plenty to keep an eye on in the next several days. I'll be keeping the comments section up to date with any potential changes.
Thank you for reading, and have a great day and a great 2013!