e australia Tropical Cyclone Edna

[Somerset Squall]

Overnight, a tiny tropical cyclone rapidly spun up a few hundred miles off the coast of Queensland. Named Edna, it had winds of 35kts this morning, but winds have since weakened to 30kts, prompting BOM to declare Edna an remnant low.  Convection was persistant over the small LLC this morning, but shear has risen which has caused the convection to flare and wane, which has caused the LLC to weaken. Ex-Edna is currently drifting west but is expected to swing north then northeast around the west side of a trough over the Coral Sea. This trough is expected to keep shear at moderate to high levels across the system, so BOM do not expect Edna to become a TC again, though they aren't ruling it out. JTWC have not recognised this system as having reached TC intensity, instead just giving the system's chances of development a MEDIUM risk.

 

An unusual track to say the least. And a blink and you'll miss it kind of cyclone, unless it comes back:

 

[Somerset Squall]

Ignore that track map now, it seems to have switched to the new low, 08U!

As for Edna, it is still just a remnant low at the moment. JTWC have downgraded development potential in the next 24 hours to LOW. Edna's remnants should continue to move north then northeast well east of Queensland.

Edited February 2, 2014 by Somerset Squall

[Somerset Squall]

Edna looks like it may become a TC again soon, convection increasing near the remnant low as it moves through the Coral Sea.

 

[Somerset Squall]

Edna has redeveloped into a tropical cyclone, with winds of 35kts. Edna has a small area of convection over the LLCC, with some limited banding features. Edna has made a large looping motion over the Coral Sea and is currently moving southwards just west of New Caledonia. Ridging to the east is expected to continue to push Edna southwards over the next few days. Shear is moderate over Edna, and as Edna is a small tropical cyclone, it isn't forecast to handle this well, and significant intensification is not expected. As Edna heads further south, shear gets stronger, and waters colder, which should eventually dissipate Edna for the second, and probably final time in about 72-96hrs.

 

[Vorticity0123]

Edna has redeveloped into a tropical cyclone, with winds of 35kts. Edna has a small area of convection over the LLCC, with some limited banding features. Edna has made a large looping motion over the Coral Sea and is currently moving southwards just west of New Caledonia. Ridging to the east is expected to continue to push Edna southwards over the next few days. Shear is moderate over Edna, and as Edna is a small tropical cyclone, it isn't forecast to handle this well, and significant intensification is not expected. As Edna heads further south, shear gets stronger, and waters colder, which should eventually dissipate Edna for the second, and probably final time in about 72-96hrs.

 

It has been an odd and exciting track of Edna, making a cyclonic turn (in SH) of more than 360* if this forecast track verifies. Edna defintely has the loop-the-loop fever! 

 

After the upgrade by JTWC, Fiji RSMC has also upgraded Edna to a tropical cyclone. The RSMC forecasts Edna not being able to curve much toward the southwest, and reaching a peak intensity of 35 kt, which is the current estimated intensity of Edna. Note that Fiji uses 10 minute mean winds (i.e. they measure the average windspeed over 10 minutes, unlike the JTWC which takes the average of 1 minute). As a rule of thumb, 10 minute mean wind speed are generally lower than 1-minute mean winds. 

 

From Wikipedia (source of this piece of text in Wikipedia itself was outdated):

 

 

Most weather agencies use the definition for sustained winds recommended by the World Meteorological Organization (WMO), which specifies measuring winds at a height of 10 metres (33 ft) for 10 minutes, and then taking the average. However, the United States National Weather Service defines sustained winds within tropical cyclones by averaging winds over a period of one minute, measured at the same 10 metres (33 ft) height.^[2] This is an important distinction, as the value of a one-minute sustained wind is 14% greater than a ten-minute sustained wind.^[3]

 

The track forecast for Edna can be seen below:

 

 

The track forecasts from both agencies are also slightly different. As noted above, RSMC Fiji forecasts a track more to the east than the JTWC does. The JTWC indicates a turn toward the soutwest at the end of the forecast period. This can be seen in the track forecast Sommerset Squall posted above.

 

This slight disagreement does have some impact in the areas being affected by the cyclone. However, it is very important not to focus on the exact track forecast regarding the system. This is especially the case with Edna, as wind shear could blow the convection associated with Edna far from the Low Level Circulation Center. The current upper-level winds (250 hPa) just south of Noumea are from the northwest, meaning that the convection (and thus precipiation) would be sheared ahead of the LLCC toward the southeast. Note that this observation is no gurantee for the future, and the direction and intensity of the upper-level winds may very well be from a completely different direction and intensity once Edna reaches the area south of Noumea.

 

Aside from the forecasted shear, Edna does seem to be fairy well-organized. The system consists of a northwest-to-southeast elongated blob of convection with some well-defined banding spiralling in from the north and south. A Rainbow satellite image of Edna can be seen below:

 

 

 

It will be interesting to see how Edna will evolve during the next few days. An exciting cyclone it has been so far! 

 

EDIT: While writing the last piece of the post, I took a look at CIMSS. To my surprise, tenacious Edna seems to have put up a burst of rapid intensification! Satellite intensity estimates from CIMSS were 66 and 60 kt from AMSU and SATCON, respectively. ADT intensity estimates have been at 49 kt, but they seem to have a generally low bias regarding tropical cyclones in the southern Pacific. (from personal experience this season).

 

To confirm the intensification trend, check the CIMSS ADT intensity graph below:

 

 

A clear upward trend in intensity estimates can be seen, indicative of at least steady intensification occuring.

 

Concluding, Edna surely has been a tenacious cyclone thus far . I think we will see a rather robust intensity upgrade from the JTWC in the next forecast cycle!

 

Sources:

http://www.met.gov.fj/

http://en.wikipedia.org/wiki/Maximum_sustained_wind#cite_note-3

http://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=-192.01,-16.16,614

http://www.ssd.noaa.gov/PS/TROP/floaters/12P/12P_floater.html

http://tropic.ssec.wisc.edu/#

Edited February 4, 2014 by Vorticity0123

[Somerset Squall]

Edna peaked at 50kts. Shear has since battered Edna, and JTWC have issued their last advisory, bringing winds down to 35kts. The circulation is unravelling under the strong shear, and the convection has completely departed the LLCC. Regeneration is not expected as Edna continues to slip polewards.