Public Advisory Edit
TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 2
WIKI-HURRICANES FORECASTING CENTER
6:00 PM JST TUE JUN 30 2015
...TROPICAL STORM CHAN-HOM CONTINUES WEST-NORTHWEST...
SUMMARY OF 6:00 PM JST...08:00 UTC...INFORMATION
CENTER POSITION CONFIDENCE: LOW
ABOUT 255 MI...410 KM NE OF PALIKIR, MICRONESIA
MAXIMUM SUSTAINED WINDS...35 KT...40 MPH...65 KM/H
MINIMUM BAROMETRIC PRESSURE...1003 MB...29.64 INCHES
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 2 KT...2 MPH...4 KM/H
DISCUSSION AND 48-HOUR OUTLOOK
At 6:00 pm JST, the center of Tropical Storm Chan-Hom was situated near 9.5N 160.0E. Maximum sustained winds were 35 knots (40 mph, 65 km/h), with higher gusts. The minimum barometric pressure was 1003 mb (29.64 inHg), and the cyclone was tracking slowly west-northwestward at 2 kt (2 mph, 4 km/h). Atmospheric conditions are expected to be quite favorable for further development of the system over the coming days as moves across the open West Pacific. A typhoon is possible on Wednesday or Thursday.
Next complete advisory at 12:00 am JST.
TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 2
WIKI-HURRICANES FORECASTING CENTER
6:00 PM JST TUE JUN 30 2015
...CORRECTED MPH CONVERSION.....
Latest satellite imagery indicates Chan-Hom has not become better organized. In fact, the center became somewhat exposed, which showed that the center was .3 south of the 3z position, and this will be correct in the best track, though latest satellite imagery suggest that the circulation has reformed to the east is now fully embedded in the convection and thus promotes intensification. Some dry air appears to have gotten in the system at around 5z, which is not surprising given the large and rather impressive outflow channels. A 0400z fix yielded a DT of 2.5 based on .35 banding and in accordance with a PT of T2.5/35 knots. A 2332z fix from SAB went with T1.5/25 kt while JTWC went with T1.0/20 knt. At 0530z, SAB went with T1.5 while the JTWC went with T1.0, even though the JTWC noted that there was .2 banding, which usually supports T2.0. It is worth noting that Dvorak intensity estimates from SAB and JTWC can from time to time have a low bias in this basin in weaker tropical cyclones, unlike the East Pacific. Since I inherited a 35 knot system, the intensity remains 35 knts.
Chan-hom, an ugly name, has a semi-complex forecast. Most computer models seem to agree that we will see a west-northwesterly direction. The 18z GFS showed 922 mbar tropical cyclone ealry next week, and showed steady development in the short term on a northwesterly course. The 0z GFS was slower, and more southerly in the short-term, but showed the same general thing. Now here is where it gets hairy. To its west, there is another of disturbed weather that it could interact with. The 12z and 0z CMC, 0z UKMET, 18z and 0z GFS ensemble mean, yesterday's HWRF westerly disturbance's grid the aforementioned GFS runs all show Chan-hom eating the westerly disturbance for dinner. However, the 12z European run is the million dollar wildcard. The 12z run ECMWF, the best model, shows the opposite and has newly-formed Chan-hom being lunch for the westerly disturbance. This is an outlier and the forecast track does not reflect and the intensity assumes this will not verify. The more recent 0z ECMWF in fact went back to what is more in line with the GFS runs. The NOGAPS I believe, as well as the Chan-home grid of an earlier HWRF run, and the 0z HWRF grid of the westerly disturbance keeps the two systems separate, but this is somewhat unlikely due to the close proximity of the two systems, and keep in mind that this should be the dominant circulation due to its strength. Another option as suggested by the 18z HWRF is that the systems stay separate, but the westerly disturbance is the dominant circulation; however, this at this time is considered an outlier due to the present setup.
Another question is how will this interact with another disturbance to the west that the 18z and 0z GFS also have this cyclone absorbing. However, this merger is still several days out, and the last several Euro, NOGAPS, UKMET, and CMC runs have more often than not kept it separate. The PTPC model is on the northern side of the guidance envelope, but since it is initialized way too north, this is considered a northern outlier. The new forecast track is slower due to projected interactions, and unlike the previous forecast, which was on the south end of the guidance, since the envelope is a bit south of the previous advisory, the new track is slighlty to the north and is closer to the GFS/ECMWF.
Our new tropical storm is located in quite a favorable environment. Wind shear is in the 10 to 15 range per the CIMSS, mostly from the southeast, which explains the displacement of convection to the west and the re-forming centers. The GFS and ECMWF show a decline in wind shear over the system, and CIMSS has the storm moving in a lower shear environment three days from now. The reason for the decline is due to the expected arrival of anticyclonic flow aloft, aideded northward-moving upper-level low to the cyclone's northeast which should provide an excellent poleward outflow channel in a day or so. Despite the ongoing and rapidly developing El Nino event, SST's on its track are near 29C, and are forecast to only get warmer during its forecast track. In addition, oceanic heat content is very high, and not high enough for it to start upwelling cold water, provided it does not stall of course, which no model shows right now. Owing to the low-latitudes that Chan-hom is in, dry air, while affecting it currently, should not prevent the storm for becoming a well-formed tropical cyclone down the road. Given the increased confidence for intensification both short-term and long-term, the new forecast intensity is raised a bit from the previous package. After 48-72 hours, the intensification rate is expected to increase, due to even more favorable conditions and as usual, is on the high-end of the guidance. The new forecast calls for an intensity of 100 knts at day 5. This forecast assumes that the interaction with disturbances to its west will not affect it in terms of intensity. The intensity forecast is somewhat uncertain, since we do not how fast the storm will build an inner core and how strong it will get before fully building an inner core.
INIT 30/0900Z 9.5N 160.0E 35 KT 40 MPH
12H 30/1800Z 9.8N 159.5E 45 KT 50 MPH
24H 01/0600Z 10.1N 159.0E 50 KT 50 MPH
36H 01/1800Z 10.3N 157.4E 55 KT 60 MPH
48H 02/0600Z 10.5N 155.7E 60 KT 70 MPH
72H 03/0600Z 11.5N 148.6E 70 KT 80 MPH
96H 04/0600Z 12.5N 146.8E 85 KT 100 MPH
120H 05/0600Z 13.6N 146.0E 100 KT 115 MPH