A week after the event, now that our power has been restored, internet seems back to normal, and our cleanup is mostly complete, I can turn to an analysis of Tropical Cyclone Marcia. Much initial analysis has been done, especially by Jen Marohasy at http://jennifermarohasy.com/jenns-blog/ who was in contact with me soon after the cyclone, and also by the Cyclone Testing Station of James Cook University.
However, perhaps I can add to the discussion with some additional suggestions and some personal observations. I was there. The eye passed over our house for about 25 to 30 minutes. I have felt the impact in Rockhampton, experienced the electricity supply loss for 6 days and 6 hours, and cleaned up tree damage to our own 1.5 acre block, the local Heritage Village and a nursing home where a family member is resident. Close family members were also without power. I can also relate the experience to previous cyclones when I lived in the Mackay area.
Tropical Cyclone Marcia was a very small, intense, and short lived Complex Cyclone, with maximum winds about 30 – 40 km away from the centre, and well outside the eye wall. At all times the Bureau of Meteorology was reporting its strength as at least one Category (more likely two) above what ground observations showed. There is no surface evidence to show it was ever Category 5. The only surface observation available indicates Category 3.
I watched on various websites the approach of TC Marcia throughout the day on Thursday 19th, and every couple of hours that night (few people got much sleep), and for as long as I had landline and then mobile internet connection (and power in my laptop) on Friday 20th.
Marcia rapidly intensified during Thursday. By 5.30pm it was near Creal Reef and about 175 km northeast of Mackay with a clearly visible eye on weather radar.
The Tropical Cyclone Technical Bulletin reported it as having central pressure 958 hPa, 10 minute winds of 155 kmh and gusts to 220 kmh. By 10.22pm it had central pressure 940hPa, winds 195 kmh with gusts to 270 kmh, and had slowed to 7 kmh but heading southwest, straight for Mackay.
By 3.20 am on Friday it was just to the east of the Percy Islands, where Middle Percy Island recorded winds from the south at 145 kmh gusting to 180 kmh. The maximum winds here were reached between 4.00 and 4.30 am when winds reached 156 kmh gusting to 208 kmh. Central pressure was 971.6 hPa. It is interesting to note that the apparent temperature was 1.3 degrees C- it is very cold in a cyclone if exposed to the wind.
Strongest winds and heaviest rainfall are usually in the eyewall. Notice that the heaviest rain in the above image (yellow) is to the west of the eye- in the vicinity of Middle Percy Island. This is what made me strongly doubt the forecast strength. The Technical Bulletin reported it as having central pressure 929 hPa, winds 205 kmh gusting to 285 kmh, moving south at 13 kmh- straight towards Rockhampton.
The next image is from 6.00 am, about two hours before landfall, travelling south at 30 kmh.
Again note the heaviest rain outside and to the west of the eye wall. The eye is about 25 km across.
Here is an interesting model of winds around Marcia when close to crossing the coast at 7.00 am on http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=143.66,-20.38,1821.
Strongest winds are shaded red. Interestingly, they are to the northwest and northeast of the eye. (Note also the deep trough from the Sunshine Coast to the border.)
After this I was busily checking final preparations, having breakfast, and making and receiving phone calls, as well as watching the websites. By 10.00 am the wind was becoming much stronger, and the Bureau was still saying it was Cat 5 and heading straight for Rocky.
Here is the radar image:
Note the yellow area of heavy rain (and presumably strongest winds) south of Samuel Hill and close to Byfield.
The wind strengthened and was at its strongest by about 12.30 pm, consistently from the east. There was one final prolonged gust, the strongest, at about 12.35 and then from about 12.50 the wind died away to nothing by 12.55 pm. Like many others I went outside and had a look around, but didn’t go far. It was raining lightly, heavily overcast, with puffs of wind from different directions. At 1.25 pm we could hear the wind coming, and it picked up again over about five minutes, blowing directly from the west, but didn’t reach the same strength as before. At a speed of 22 kmh, the eye was about 11 km across at this stage. This screenshot shows the eye right over us at about 1.10 pm.
The eye is just visible, and strongest rain and winds are to the south and east.
But this one shows it just 10 minutes later:
Note the eye has disappeared- it collapsed while over us.
Rockhampton Airport is about 12km south-southwest, so 30 minutes later the eye should have reached there. But it didn’t. Here is a screenshot of observations at Rocky Aero from 12.41 to 4.30 pm.
I have circled key information. At 12.50 pm the wind was ESE at 72 kmh, with a gust to 113 kmh. Between 1.13 and 1.52 (arrowed) the wind swung from SE to WSW, but never dropped below 24 kmh. Lowest pressure was 975.7 hPa. The wind steadily picked up and was strongest around 2.45 to 3.00 pm, reaching 82 kmh with a gust to 113 kmh. This was different from my experience, where the wind was consistently from the east, then very light and variable, then directly from the west, but not as a strong. The eye had collapsed before the centre was near the airport, and the remnants passed a couple of kilometres to the east. The cyclone was rapidly degrading.
My last screenshot before the internet died and my battery went flat, shows the BOM forecast at 2.12pm:
It shows Marcia still Cat 3 at 2.00 pm. But Rocky Aero data show winds were no more than Category 1 at this time. At our place, the winds at this time were from the west and still damaging trees but not nearly as strong as before the eye passed. By 3.00pm the winds were light and we were out in the street talking with the neighbours.
On eastern slopes or hills, and closer to the coast, winds would have been much higher. I estimate gusts at our place, funnelled up a gully on an east facing slope, were around 120 – 130 kmh- similar to our experience of TC Ului at Sarina some years ago.
The Cyclone Testing Station of James Cook University has released a preliminary report at https://www.dropbox.com/s/9y8hdb74ycgemfi/TC%20Marcia%20Rapid%20Assessment%20Report%2020_02_2015.pdf?dl=0 . They will produce more definitive analysis in a few weeks.
To summarise, this report states Yeppoon experienced Category 2 winds, and Rockhampton Category 1. The report goes on to state:
“A community that receives an over-represented wind speed report may have potential for complacency in preparation or building standards in the future. Further research is required to determine if this is an issue.”
But was TC Marcia a Complex Cyclone, one in which maximum winds are concentrated away from the eye? All radar images show heaviest rain, and therefore probably winds, away from the eye wall.
Byfield community is 30 km northwest of Yeppoon, half way between Yeppoon and Samuel Hill. There are reports of every tree stripped for kilometres, which appears to indicate strong Cat 3 to Cat 4 winds. Radar image at 10.10 am shows heaviest rain just to the west of Byfield and just to the south of Samuel Hill. Yet Samuel Hill did not experience winds of this strength.
And here’s a photo of part of our block taken at 3.30 on the afternoon Marcia passed.
Note every tree has at least 50% of its leaves stripped and several branches off, and several were completely uprooted, and these are tough old ironbarks. So allowing for 30 km closer to the sea and two hours earlier, I wouldn’t be surprised if winds were 150 – 160 kmh at Byfield- but not 200 kmh.
Until JCU can do their complete assessment, we will not know exactly what happened. No doubt their engineers will also visit Stanage Bay, where Marcia crossed the coast. Tropical Cyclone Marcia was a very small, intense, and short lived Complex Cyclone, with maximum winds about 30 – 40 km away from the centre, and well outside the eye wall. At no time was it Category 5. Despite its relative weakness compared to some other cyclones, Marcia did tremendous damage in Central Queensland.
The main thing is no one was hurt.
kenskingdom 