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Public advisoryEdit

TYPHOON CHAN-HOM PUBLIC ADVISORY NUMBER 26

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST MON JUL 06 2015

...CHAN-HOM REACHES TYPHOON STATUS...

SUMMARY OF 6:00 PM JST...09:00 UTC...INFORMATION

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LOCATION...17.1N 140.5E

CENTER POSITION CONFIDENCE: ZERO

ABOUT 340 MI...544 KM WNW OF SAIPAN, MARIANA ISLANDS

MAXIMUM SUSTAINED WINDS...65 KT...75 MPH...120 KM/H

MINIMUM BAROMETRIC PRESSURE...978 MB...28.88 INCHES

PRESENT MOVEMENT...WNW AT 10 KT...12 MPH...19 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 6:00 pm JST, the center of Typhoon Chan-hom was situated near 17.1N 140.5E, about 335 miles (540 km) west-northwest of Saipan, Mariana Islands. Maximum sustained winds were 65 knots (75 mph, 120 km/h), with higher gusts. The minimum barometric pressure was 978 millibars (hPa; 29.88 inHg), and the cyclone was tracking west-northwest at 10 knots (12 mph, 19 km/h). Environmental conditions are expected to favor steady to rapid intensification over the next 48 hours, and Chan-hom is likely to become a powerful cyclone over the West Pacific.

NEXT ADVISORY

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Next complete advisory at 12:00 am JST.

$$

Forecaster YE

DiscussionEdit

TYPHOON CHAN-HOM PUBLIC DISCUSSION NUMBER 26

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST MON JUL 06 2015

Chan-hom has that WPAC/glory era ATL look to it. Very impressive spiral banding has developed over the past 24 hours, although microwave imagery suggests that the core is not well-organized due to some dry air first noted by my boy TheAustinMan in a very early discussion and correctly depicted by the HWRF. While over the last couple hours the banding is not well defined, it still arguably wraps over 100% of the center. The outflow channels of this typhoon is very impressive in all directions, towards both the equators and the poles. Two UW-CIMSS AMSU passes supported an intensity of 75 and 67 knts, but CI values from the JTWC at 0532z are T4.0/65 knts and T3.5/55 knts from SAB a few hours before the JTWC fix. Given the low bias of Dvorak so far with this system as evident by ASCAT passes the past few days, and the storms so-so inner core, I am inclined to believe that in this force of nature, there is a small area of hurricane-force winds. Therefore, the intensity has generously been increased to 65 knts. This estimate is more uncertain than normal due to the fact that the Dvorak technique struggles with storms in the T3.5-T4.0 range. Instances of this include Tropical Storm Bonnie in 2004 and Hurricane Polo in 2014.

While the inner core is not the greatest, it is getting better but dry slots have limited development, and a dry slot currently is apparent. However, we are in a historic pulse of the MJO, so dry air is not likely to be a serious problem if one at all once it has a good looking inner core. I expect this to take another -12 hours, so little change in strength is expected this evening. Overnight, its inner core will have finished construction, and true rapid deepening, which has been anticipated for like days now, is expected to start at last. While systems like these can and do intensify 60+ knts in a day, the WFHC forecast below does not intensify that fast, due to uncertainties over the exact timing of the RI event, and only shows 30 knt a day, which is still fairly fast, through 48-72 hours.

In longer time frames, the GFS, ECMWF, and HWRF all continue to strongly suggest that Chan-hom will attain Category 5 intensity over the coming days, and as such the WFHC brings the storm to 140 knts by day 3, before weakening it slightly to a likely eyewall replacement cyclone on day 4. Rapid weakening, of course, is expected once Chan-hom moves inland.

As noted in past packages, Chan-hom continues to track steadily west-northwest under the influence of a potent mid-level ridge to the cyclone's north. This steering mechanism is expected to dominate the forecast period, and very little change in trajectory is expected. However, it's worth noting that the GFS and HWRF have shifted slightly south over the previous runs, and the updated WHFC track forecast has been nudged in that direction. On the forecast path, Chan-hom is expected to pass closest to the southern Japanese Islands in 96 hours or so before tracking directly into mainland China by day 5. All indications are that Chan-hom will pose an extreme threat to the China mainland by the end of the week. Residents both in the southern Japanese Islands and China should very closely monitor the progress of what is expected to be a large and powerful cyclone.

INIT 06/0900Z 17.1N 140.7E 65 KT 75 MPH

12H 06/1800Z 17.7N 138.4E 70 KT 80 MPH

24H 07/0600Z 18.5N 136.9E 85 KT 100 MPH

36H 07/1800Z 19.5N 135.1E 100 KT 115 MPH

48H 08/0600Z 20.7N 133.2E 115 KT 140 MPH

72H 09/0600Z 23.2N 128.9E 140 KT 160 MPH

96H 10/0600Z 26.3N 124.5E 135 KT 150 MPH

120H 11/0600Z 29.4N 121.3E 65 KT 75 MPH...INLAND

$$

Forecaster YE

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