How did the Observatory fare in signal issuance for Linfa and Nangka?

Now that Linfa and Nangka are gone, let's review them and see how well the Observatory performed in these two cases. Before reading further, just mind you that unavoidably this has to be a rather subjective article - but as always we welcome your comments. :)

Track of Linfa

Track of Nangka

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Severe Tropical Storm Linfa

#1 Standby Signal:
Issued at 10:40 am on 20th June 2009 @ 370 km ESE of HK (STS)
Cancelled at 5:45 am on 21st June 2009 @ 420 km E of HK (STS)

Timing	6
Effectiveness	8
Higher signal indication	10
Cancelling	7

Not issuing #3 Strong Wind Signal

Appropriateness

10

Some other scores:

Forecast track accuracy	6
General performance	8

Comments about the signals:

Timing: Not a terrible timing for issuing the #1 signal, but the Observatory had a better choice before that. Linfa was travelling north in the night of 19th, and there were obvious NW jogs in the interim. The structure of Linfa was improving that night and the Observatory upgraded it into a severe tropical storm near midnight between 19th and 20th. The Observatory would have better justification if it had decided to issue at that time, rather than at quite an embarrassing 10:40 am which was almost the time that the storm ceased NW movements and that of the closest point of approach.

Effectiveness: This #1 was enough to warn people offshore to take care of the possible swells.

Higher signal indication: The Observatory said that #3 would not be necessary on the 20th and, well, that was a good enough indication wasn't it? The storm did not cause any more trouble to the signal-issuing agency as it moved away from us later the day.

Cancelling: I think that the Observatory lifted the signal because it reached the latitude of Hong Kong, i.e. 22.3 degrees North, and due west movement is extremely unlikely. However, in terms of distance from Hong Kong, the storm did not move away quickly from Hong Kong after the signal was removed, and in fact remained within 600 km from Hong Kong throughout June 21st.

Not issuing a higher signal: There couldn't be any doubt about it - by no means was a #3 necessary.

Verdict:

It seems that the Observatory was quite confident that it would move away from HK as seen from its earlier forecasts. However it finally succumbed to its poleward turn and as it jogs NW while it intensified it became increasingly difficult for them not to issue the signal. Nevertheless the storm moved slowly and in any case the Observatory would have sufficient time to make its decision. It remained a question as to what the internal requirements for #1 to be issued are.

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Tropical Storm Nangka

#1 Standby Signal:
Issued at 7:15 am on 26th June 2009 @ 420 km SSE of HK (TS)

Timing	5
Effectiveness	7
Higher signal indication	8
Cancelling	-

#3 Strong Wind Signal
Issed at 3:40 pm on 26th June 2009 @ 220 km SE of HK (TS)
Cancelled at 5:45 am on 27th June 2009 @ 90 km NNE of HK (TD)

Timing	8
Effectiveness	6
Higher signal indication	10
Cancelling	9

Not issuing #8 Gale or Storm Signal

Appropriateness

10

Some other scores:

Forecast track accuracy	7
General performance	7

Comments about the signals:

Timing: #1 was a bit late - for those who have already left home for work or school, they might not even know that a storm is coming their way. Based on the high speed of the storm, #1 should have been issued earlier although it was a marginal TS. For the #3 signal the decision was probably OK.

Effectiveness: The #1 mainly served as a basis for the upgrade to #3. For #3, the correct signal was issued based on its proximity to Hong Kong; however it turned out that the storm was so weak that this might be one of the weakest #3 signals ever issued.

Higher signal indication: The Observatory was in general consistent in announcing the possibility of #3 when it issued #1 - it first said that "#3 not likely in the morning and early afternoon", and when afternoon came it was evident that Nangka would be close enough to justify a #3, hence the words "will consider in 2-3 hours". Finally #3 was raised two hours later. For the possibility of higher signals after #3 was issued, the Observatory was very smart to add a condition for #8 to be necessitated, but unfortunately, in an attempt to save time and words, some media truncated the condition and simply referred to the chance of #8 as slim.

Cancelling: A reasonable time to lift the #3 signal - in fact only Tate's Cairn and Ngong Ping (both on very high grounds) recorded sustained strong winds after midnight. Could have been lowered even earlier, but there were no problems for the chosen time 5:45 am either.

Not issuing a higher signal: #8 was absolutely not necessary in this case.

Verdict:

Perhaps inspired by Fengshen last year, the Observatory was one of the earliest (among the international community) to revise its track westward and westward, but on absolute scale the track error was rather large (but not unacceptable), and hence I give it a rating of 7. It was a bit unlucky for it being one of the calmest #3 signals, but it's always better safe than sorry right?