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Tropical weather analysis - November 6, 2013

By: KoritheMan , 2:21 AM GMT on November 07, 2013


Dangerous Super Typhoon Haiyan is heading steadily toward the central Philippines. As of the latest JTWC advisory, the following information was available on the typhoon:

Wind: 175 mph, with higher gusts
Location: 8.6°N 132.8°E
Movement: WNW at 18 mph
Pressure: 911 mb
Category: 5 (Saffir-Simpson Hurricane Wind Scale)

The satellite presentation is, in a word, spectacular. After a brief hiccup in the southern eyewall from about 2000 to about 2315 UTC, convection has redeveloped around the southern eye, and Haiyan appears to be on course to maintain its intensity. Upper-level outflow is exceptionally well-defined everywhere except the east, where it is somewhat restricted, but expanding. In addition, a large convective band extends to the west of the center; given the small size of the cyclone, it is presumed that there are no tropical storm force sustained winds occurring within this band, although scatterometer data suggests that the winds could be sustained at 25 to 35 mph in that band.

Figure 1. Latest infrared satellite image of Super Typhoon Haiyan. Image credit: NOAA's Satellite Services Division (SSD).

There do not appear to be any obvious factors to immediately weaken Haiyan. Oceanic heat content in this portion of the western Pacific is extremely significant; in addition, the near-storm vertical shear appears to be low as evidenced by the well-organized cloud and outflow patterns, and there does not appear to be any dry air that could get entrained into the circulation. The one fly in the ointment that is, unfortunately, extremely difficult to predict but common of intense typhoons like Haiyan, is a possible eyewall replacement cycles, or even multiple ones. I have literally no skill to anticipate these changes, and neither do any of the global and dynamical models. Primarily because of this ignorance, my forecast will keep Haiyan at 150 kt during the next 12 hours, followed by slow weakening after that as Haiyan interacts with land and possibly undergoes a concentric eyewall cycle (based primarily on timing, as cyclones this intense cannot normally maintain such obscene intensities for very long). However, I want to emphasize that I expect Haiyan to be at or near Category 5 intensity (Saffir-Simpson Hurricane Wind Scale) at landfall. Of course, there is enough uncertainty in the inner core evolution of such an intense typhoon that the winds could theoretically be 20 to 30 mph lower at landfall. Once the cyclone emerges over the South China Sea, a steady weakening trend is expected as dry air and subsident flow increases and oceanic heat content drops off sharply west of 115°E. There does not appear to be a lot of vertical shear over the South China Sea in the GFS model fields during those time ranges, but shear forecasts are riddled with immense uncertainty even a day out, and I would not be surprised if southwesterly shear increased even modestly ahead of the next upper-level trough. It should be noted that my forecast track and the JTWC track takes Haiyan inland over Vietnam to a position where the cyclone center lies in close proximity to the adjacent South China Sea, which could help to promote sustained tropical storm force winds along the coast all the way up to day five in the forecast period, and that is reflected below.

Haiyan appears to be moving quickly west-northwest, and is more or less on track. The strong subtropical ridge to the north extends all the way into the upper troposphere, and Haiyan will follow its southern periphery over the next several days, making landfall in the central Philippines by Thursday evening (United States local time). After that time, the typhoon is forecast to continue heading in that general direction while steadily gaining additional latitude. Beyond about 48 hours, an upper-level trough over China is expected to weaken the ridge a little and cause Haiyan to slow its forward speed. Landfall is likely to occur at or just after 72 hours in northern Vietnam. My forecast track is in good agreement with the 18z GFS, and is fairly similar to the latest JTWC track.

Haiyan passed not too far to the north of the island of Palau around 15 or 16 UTC, and the southern eyewall raked the island. While damage is by no means going to be catastrophic on the island (we're talking about a westward-moving typhoon, which would tend to idealize the strongest winds to the northern eyewall) and especially compared to what it will be farther west, damage was undoubtedly significant on the northern reaches of the island, where sustained winds probably reached 80 to 100 mph. We will need to wait a few days before the extent of the damage on the island can be determined.

Haiyan is a fairly small tropical cyclone, with 34 kt winds extending outward only up to perhaps no more than about 130 miles in the northeastern semicircle. Since the cyclone will be slow to gain latitude, and will only barely be above 10°N at landfall in the Philippines, I do not imagine we will see a Katrina or Ike-size storm hitting the Philippines. If true, this means that the core of strongest winds will be confined to a fairly small area along the northern and northeastern eyewall. However, if a concentric eyewall cycle occurs prior to or just after landfall, the outer wind radii will increase, spreading out damaging winds over a larger area. Rainfall and flooding should be fairly limited over the Philippines due to the fast forward motion of Haiyan; however, the rains could be heavier and cause extensive flooding over Vietnam, when the cyclone is likely to encounter an upper-level trough and decelerate.

Intensity forecast and positions

INITIAL 11/07 0000Z 8.7°N 133.8°E 150 KT 175 MPH
12 hour 11/07 1200Z 9.5°N 128.3°E 150 KT 175 MPH
24 hour 11/08 0000Z 10.9°N 124.1°E 135 KT 155 MPH...INLAND
36 hour 11/08 1200Z 11.9°N 120.1°E 120 KT 140 MPH...OVER WATER
48 hour 11/09 0000Z 14.9°N 114.2°E 105 KT 120 MPH
72 hour 11/10 0000Z 90 KT 105 MPH
96 hour 11/11 0000Z 65 KT 75 MPH...INLAND
120hour 11/12 0000Z 35 KT 40 MPH...INLAND

Track forecast

Figure 2. My forecast track for Haiyan. Note that I couldn't find a track map other than the one I found above, so because of the limitations of that map, I am unable to assess latitudinal and longitudinal points subsequent to the 48 hour mark, but my forecast track is pretty similar to the JTWC at later periods.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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5. WunderAlertBot (Admin)
3:51 AM GMT on November 19, 2013
KoritheMan has created a new entry.
4. Astrometeor
4:24 AM GMT on November 08, 2013
Quoting 3. wxchaser97:
Where did you get the tracking map for the WPAC? It's better than anything I have for that part of the world.

Trade secret.
Member Since: December 31, 1969 Posts: Comments:
3. wxchaser97
11:52 AM GMT on November 07, 2013
Where did you get the tracking map for the WPAC? It's better than anything I have for that part of the world.
Member Since: December 31, 1969 Posts: Comments:
2. DaveFive
8:39 AM GMT on November 07, 2013
Hello KoritheMan,I am Dave from SanJose, CA. I have enjoyed reading your blog on the hurricane as well as the photos. The weather here in San Jose has been fair and dry since April.
Member Since: December 31, 1969 Posts: Comments:
1. LemieT
4:06 AM GMT on November 07, 2013
Nice work and well written. These Typhoons make me have major WPAC envy. On the other hand the loss of life is always very saddening.
Member Since: December 31, 1969 Posts: Comments:

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