TC Debbie

TC Debbie hit the Whitsunday coast and areas to the south and inland yesterday.  As I spent nearly half my life in places not far from Mackay and have many friends in the region, I was very interested to see what was happening.   I began checking online from 5 a.m. Tuesday morning.

Here is some initial analysis of TC Debbie.  Firstly, here is the table of cyclone intensities as found at http://www.bom.gov.au/cyclone/faq/index.shtml#definitions .

Fig. 1:  Cyclone Intensity

TC Intensity

I began checking online from 5 a.m. Tuesday morning.

Fig. 2:  0500 forecast cyclone track map.

Debbie 5am

How accurate was the Bureau’s forecast?  Here is the forecast 22 hours later, at 0300 Wednesday morning.

Fig. 3:  Wednesday 0300 forecast cyclone track map.

Ex TC Debbie

The track forecast was pretty good.

The next images show Debbie’s progress across the Whitsunday Islands until the eyewall crossed the coast near Airlie Beach.

Fig. 4:  0720 Eyewall about to hit Hamilton Island

radar 720am debbie hayman is eye

Fig. 5:  0910  Hamilton Island near the eyewall, Hayman Island in the eye

radar 910am debbie hamilton eyewall

Fig. 6:  10.30  Hamilton Island near the eyewall, Hayman Island in the eye, and the eyewall about to pass over Airlie Beach

radar 1030am debbie hamilton eyewall

And four and a half hours later, the worst is over at Hamilton and Hayman Island and the eye is collapsing over Proserpine.

Fig. 7:  1510  Debbie weakening near Proserpine

radar 310pm eye breakup

Note the “gap” in the image in the northwest sector.  The Bowen radar failed and the Mackay radar was blocked by high mountains to the west.

What about forecasts of the cyclone’s intensity?

The next figures show plots of wind gusts, pressure, temperature, and rain at Hamilton Island, Proserpine, and Bowen, the closest stations to the cyclone’s track.

Fig. 8:  Wind gusts at Hamilton Island

wind hamilton

The black line shows the period from just before 8.00 a.m. until about 2.30 p.m. during which Hamilton Island was close to the eyewall, the area of maximum wind strength.   For nine hours from before 6.00 a.m. until nearly 3.00 p.m. wind gusts were of Category 3 strength.  From 8.00 a.m. until 12.30 p.m. gusts approached or exceeded 225 km/hr, bordering on category 4, and between 10.35 and 10.30 reached 263 km/hr three times at least- and the Bureau had forecast winds up to 270 km/hr.  While the station at Hamilton Island is too high to be completely reliable, these data are indicative that winds at 10 metres were at cat 4 level for some time.

Fig. 9:  Air Pressure at Hamilton Island

pressure hamilton

The red line shows the period from just before 8.00 a.m. until about 2.30 p.m. during which Hamilton Island was near the eyewall, the area of maximum wind strength.    From 2.00 a.m. until 5.00 p.m.  pressure was below 985 hPa (Cat, 2) and from 10.00 a.m. until 1.30 p.m. was below 970 hPa (Cat.3) but did not reach 955 hPa (Cat. 4).  Remember however that Hamilton Island was some 50 km from the centre of the eye, so 955 hPa is quite possible for central pressure.

On the basis of wind gusts and pressure at Hamilton Island, I believe Debbie was a strong Category 3, weak Category 4 system.

Fig. 10:  Air temperature at Hamilton Island

T hamilton

Note the sudden jump in temperature from 8.12 a.m.- 3 degrees in 3 minutes- coinciding with a wind gust of 212 km/hr, and kept climbing to unbelievable values.  (Compare with Proserpine below.)  It is likely that the AWS probe malfunctioned, and failed altogether at 12.00 noon.

Fig. 11:  Rain at Hamilton Island

rain hamilton

Rain measurement is unlikely to be accurate in such ferocious winds.  Note how rainfall levelled off from 11.00 a.m until 2.00 p.m., then increased after 3.00 p.m.

Fig. 12:  Wind gusts at Proserpine

wind proserpine

Proserpine Airport is some 20 km inland, 41 km west of Hamilton Island and 56 km from Bowen.  As the cyclone arrived over land it began losing strength and the eye began to shrink.  From 10.00 a.m. until 2.00 p.m. gusts were at Category 2 strength and at 1.00 p.m. reached the magic 165 km/hr of Cat 3 strength.  They were very probably much stronger in the town itself 9.1 km north.

Fig. 13:  Pressure at Proserpine Airport

pressure proserpine

From 12.30 p.m. until 5.00 p.m. the pressure at the airport, some 20-30 km from the centre, was below the Category 3 value of 970 hPa.

Wind gust and pressure data indicate Debbie was very likely still Category 3 as it passed over Proserpine town.

Fig. 14:  Air temperature at Proserpine

T proserpine

Fairly stable temperature with only about 1.5C range all day.

Fig. 15:  Rain at Proserpine

rain proserpine

Steady rain all day, fairly typical of cyclonic conditions.  At Strathdickie not far from Proserpine, 193mm fell in one hour that morning, and at Dalrymple Heights about 50km south 814mm fell in 24 hours.

Fig. 16:  Wind gusts at Bowen

wind bowen

For four and a half hours wind gusts reached Category 2 strength, and were above 100 km/hr from 9.00 a.m. to 8.00 p.m.

Fig. 17:  Pressure at Bowen

pressure bowen

Pressure was at Category 2 levels from 9.00 a.m.

Fig. 18:  Air temperature at Bowen

T bowen

Winds were west south west most of the day, but as Debbie passed and winds turned northwest (over the ocean), the temperature climbed.

Fig. 19:  Rain at Bowen

rain bowen

Steady rain all day: 12 inches in 12 hours.

While no stations were directly in the cyclone’s path, nearby station data indicate that Debbie was a large Category 3 to Category 4 tropical cyclone when it hit the coast and brought very strong winds, very heavy rainfall, and widespread destruction.  It is still lingering as a tropical low 300 km inland, bringing more strong winds and very heavy rain, and will head south over the next couple of days.  The clean up begins.  We await the report from James Cook University engineers who will provide their assessment of damage and wind loadings in a few weeks’ time.

Give credit where credit is due: the Bureau of Meteorology got this one pretty right.

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8 Responses to “TC Debbie”

  1. siliggy Says:

    Earlier Track maps did not do so well.
    “Cape Cleveland area residents directed to evacuate”
    http://mypolice.qld.gov.au/blog/2017/03/26/cape-cleveland-area-residents-directed-evacuate/
    Alva Beach.
    Maximum wind gust 63Km/hr
    http://www.bom.gov.au/climate/dwo/IDCJDW4001.latest.shtml
    On March 26 I made this comment on Facebook.
    “Lance Pidgeon https://www.windytv.com Like moving artwork, is showing this crossing still further south of the BoM’s recently revised further south prediction. WindyTV shows landfall just north of Bowen and strong winds at Airlie Beach.”

  2. siliggy Says:

    The following morning I commented on Jennifer Marohasy’s Facebook photo of the BoM track map showing the cyclone heading for AYR. They had updated it to just North of Bowen by the time I commented.
    “Lance Pidgeon https://www.windytv.com Slide the date and time over to 12AM tuesday to see the eye pass directly over Bowen from Airlie beach. Then move it to the weekend and you will see it reform at Brisbane.”
    Windy TV now shows strong wind gusts tomorrow morning at the Gold coast as it reforms. The Bom forecast as at 6AM this morning says.
    “Friday 31 March Gold Coast area
    Partly cloudy. Very high (90%) chance of rain in the early morning. The chance of a thunderstorm in the morning. Winds easterly 30 to 45 km/h turning southerly 35 to 55 km/h before dawn then decreasing to 25 to 40 km/h in the evening.
    Large and powerful surf conditions in the afternoon and evening are expected to be hazardous for coastal activities such as rock fishing, swimming and surfing.”

    • kenskingdom Says:

      TCs and Lows are notoriously difficult to predict. Emergency services/ police were taking no chances and many areas were evacuated and it turned out there was no problem. e.g. Mackay low lying areas, about 25,000 people (not all left). I would not want to live in those areas as they are a disaster waiting to happen, and have happened in the past e.g. 1918.
      The BOM central track was pretty accurate and still is- currently the low is heading south east rapidly and the weather here in Rocky clearing as i write- even saw the sun a little while ago. Some extraordinary rain around still.
      The low could turn into an East Coast Low but not likely to reform as a tropical cyclone.

  3. wshofact Says:

    Thanks for the overview Ken – if you do drive to Brisbane – b well take care mate.

  4. siliggy Says:

    Looks like the short term peak wind gust speeds predicted by the BoM were more accurate than WindyTV. Windy was still predicting something like 137 at Hamilton island as 183 was measured. Then Bom predicted 260 and got amazingly close with 263. As you show above. WindyTV now has serious wind (132 Km/hr) near Ballina at 9PM tomorrow.

  5. Martin Clark Says:

    For north Queensland, I think things are likely to change a bit, provided JCU CTS doesn’t get muzzled.
    https://www.jcu.edu.au/cyclone-testing-station/swirlnet
    Look at the results for Tower 5, shoreline south of Bowen. Max 3 sec gust 125, low Cat 2, and Tower 6, Proserpine, 96, barely Cat 1.

    • kenskingdom Says:

      Those are interesting numbers. Remember these are at house level, not 10m, and are designed to gauge wind loading on buildings from turbulent winds around houses and vegetation. Wind speeds are measured at 10 m over flat open terrain, not ground level. It’s interesting how much difference there is. I understand this is the first Queensland cyclone in which SWIRL has been deployed. They will also gather information from damage to trees, signs, and buildings, and will use this, BOM data, and SWIRL data in their final assessment, which hopefully will improve building design and construction. It’s a shame they didn’t have a tower in Airlie.

  6. siliggy Says:

    The BoM Coral sea cyclone out look as I type says “There are currently no significant tropical systems in the Eastern Region.
    A number of weak, transient lows may develop along a trough in the far northern Coral Sea over next few days, however none is expected to develop into a cyclone.

    Likelihood of a tropical cyclone in the Eastern Region on:
    Sunday:Very Low
    Monday:Very Low
    Tuesday:Very Low
    http://www.bom.gov.au/qld/forecasts/cyclone.shtml

    WindyTV shows one at Port Vila Right now and predicts 200K plus winds by tonight. Then it shows the cyclone heading to Noumea New Caledonia. trouble there to start by late monday night.
    https://www.windytv.com

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