TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 3
WIKI-HURRICANES FORECASTING CENTER
12:00 AM JST WED JUL 01 2015
...CHAN-HOM REMAINS A DISORGANIZED SYSTEM...
SUMMARY OF 12:00 AM JST...15:00 UTC...INFORMATION
CENTER POSITION CONFIDENCE: ± 35 MI... 55 KM
ABOUT 205 MI...330KM 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 AT 9 KT...10 MPH...17 KM/H
DISCUSSION AND 48-HOUR OUTLOOK
At 12:00 am JST, the center of Tropical Storm Chan-Hom was situated near 9.8N, 159.0E, or about 205 miles (330 kilometers) northeast of Palikir, Micronesia. Maximum sustained winds were 35 knots (40 mph, 65 km/h), with higher gusts. The minimum barometric pressure was 1003 millibars (hPa; 29.64 inHg), and the cyclone was tracking west-northwestward at 9 knots (10 mph, 19 km/h). Conditions are expected to become more conducive over the coming days as Chan-Hom continues to track west-northwest, which may allow it to strengthen with greater pace.
Next complete advisory at 06:00 am JST.
TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 3
WIKI-HURRICANES FORECASTING CENTER
12:00 AM JST WED JUL 01 2015
Infrared satellite imagery over the past few hours indicates that Chan-Hom has continued to develop deep and cold convection, with cloud top-temperatures falling below -80C for a significant portion of the convective mass. Upper-level outflow also appears to be healthy for this system, with a large expanse of transverse cirrus banding expanding towards the west and north. However, microwave and scatterometer data continues to suggest that Chan-Hom remains a disorganized tropical cyclone. 89GHz microwave imagery from an 08:41z pass indicated that the center remains displaced to the southeast of the center, thoughdeveloping rainbands was also an evident feature. An 11:00z ASCAT pass confirmed the status of the disorganized center, revealing that Chan-Hom possesses an elongated center of circulation displaced to the southeast of the main convective mass. In addition, the scatterometer failed to detect any tropical-storm force winds. However, given the CIMSS-ADT intensity estimate which yielded T2.0/30kt despite the center being misplaced well east of the center, and another scatterometer pass at 10:32z that sampled a sizeable area of 35 knot winds, the intensity for this advisory has been kept at 35 knots.
Chan-Hom is currently located in an area that is only marginally favorable for intensification. Since its classification as a tropical cyclone, the center of circulation has remained displaced to the southeast or east of most of the convection as a result of 20-30 knot southeasterly wind shear originating from just east of Chan-Hom. However, conditions are expected to gradually become much more favorable for development as Chan-Hom moves west-northwestward. Wind shear across a large area surrounding the Northern Mariana Islands, where Chan-Hom is expected to track near, is largely below 15 knots, which, provided that the tropical cyclone is able to withstand light to moderate shear, should allow for an increased rate of strengthening. Sea surface temperatures and oceanic heat content in the general path of the tropical cyclone are also very high. The subtropical flow and upper-level low later in the week discussed in the previous two advisories continue to be suggested by the computer models and should allow for improved outflow, which should aid in strengthening. Dry air is not expected to inhibit intensification at this time, though the passage of an upper-level low to the north of Chan-Hom later this week may be the catalyst for some dry air entrainment as suggested by the HWRF. However, given the overall conducive environment, the intensity forecast for this advisory will continue the forecast philosophy that Chan-Hom will steadily intensify without much inhibition to a strong typhoon at the end of the forecast period, maintaining the thinking held during the last advisory. However, many of the atmospheric parameters determining Chan-Hom's intensity may change significantly if a developing tropical disturbance to the west becomes a tropical cyclone itself, a possibility which continues to complicate the forecast for Chan-Hom.
The present motion for Chan-Hom has been set to around 285/9, suggesting that Chan-Hom is accelerating towards the west-northwest as it gains in latitutde away from the monsoon trough. Present steering for the tropical cyclone is domniated by a subtropical ridge to its north, which should continue to steer Chan-Hom towards the west or west-northwest for the next 24-36 hours, a scenario that the models are generally in consensus about. However, the models significantly diverge after 36 hours and the track forecast becomes increasingly complicated as a result of an area of low-pressure to Chan-Hom's west that is forecast by most of the models to become a tropical cyclone itself. Chan-Hom's close passage of this developing system will inevitably lead to a Fujiwhara interaction, which will generally cause Chan-Hom to be tugged slightly to the southwest and the other system slightly to the northeast. However, the significance of this interaction differs between the models and plays a large role in the long-term track forecast. Given that Chan-Hom is already a tropical cyclone, Chan-Hom's track will probably be less affected than the other developing disturbance, so the 6z NAVGEM run (which shows Chan-Hom merging into the disturbance) and the 12z JMA run (which does not initialize Chan-Hom at all) can be discarded. The other models suggest the aforementioned tug southwestward before the storm resumes its previous course, but they also show the developing system merging with Chan-Hom. The GFS, CMC, and IFS models are in general agreement that Chan-Hom will traverse through the Northern Mariana later in the week as a strong typhoon, and as these models appear to show the most realistic short-term track guidance, the current WHFC forecast track is aligned with this guidance.
INIT 30/1500Z 9.8N 159.0E 35 KT 40 MPH
12H 01/0000Z 10.1N 157.8E 40 KT 45 MPH
24H 01/1200Z 10.5N 157.0E 45 KT 50 MPH
36H 02/0000Z 11.3N 154.5E 55 KT 60 MPH
48H 02/1200Z 11.2N 152.4E 60 KT 70 MPH
72H 03/1200Z 12.0N 147.8E 70 KT 80 MPH
96H 04/1200Z 14.1N 146.5E 90 KT 105 MPH
120H 05/1200Z 16.9N 144.5E 100 KT 115 MPH