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Public advisoryEdit

TYPHOON NANGKA PUBLIC ADVISORY NUMBER 17

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST TUE JUL 07 2015

...TYPHOON NANGKA EXPLODING...NEARLY A SUPER TYPHOON...

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

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LOCATION...13.9N 153.8E

CENTER POSITION CONFIDENCE: VERY HIGH

ABOUT 630 MI...1,010 KM ESE OF SAIPAN, MARIANA ISLANDS

MAXIMUM SUSTAINED WINDS...125 KT...145 MPH...230 KM/H

MINIMUM BAROMETRIC PRESSURE...926 MB...27.34 INCHES

PRESENT MOVEMENT...W AT 11 KT...13 MPH...21 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 6:00 pm JST, the center of Typhoon Nangka was situated near 13.9N 153.8E, or about 635 miles (1,020 km) east-southeast of Saipan, Mariana Islands. Maximum sustained winds were 125 knots (145 mph, 230 km/h), with higher gusts. The minimum barometric pressure was 926 millibars (hPa; 27.34 inHg), and the cyclone was tracking west at 11 knots (13 mph, 21 km/h). Continued rapid intensification is expected overnight.

NEXT ADVISORY

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Next complete advisory at 12:00 am JST.

$$

Forecaster YE

DiscussionEdit

TYPHOON NANGKA DISCUSSION NUMBER 17

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST TUE JUL 07 2015

Typhoon Nangka is still intensifying rapidly. A WMG eye has not only developed but persisted, and while the eye temperature has fluctuated like they usually do in intense tropical cyclones, has been as warm as 16C, which in this basin, is typically reserved for super typhoons. While a AMSU microwave pass found at 0330z an open eyewall to the south, this is not supported by visible satellite loops. Even though Nangka remains somewhat asymmetrical, the CDO has become more smooth and consolidated, and on Dvorak IR, a W ring has developed around a WMG eye and while no official fixes have been made, I am suspect that Nangka is in the ballpark of T6.5-T7.0/127-140 knts at the upcoming frame, depending on how the W ring persists. In addition, to the W ring, there is a nice burst of deep convection that my still march around the track further of sub- -75C cloud tops (CMG). Anyhow, the eye has also becoming more circular and less elongated, although it could still become more defined. Looking st the latest imagery, Nangka has a stadium effect to it, a feature typically observed in powerful tropical cyclones. Upper-level outflow is good in all directions and favors more intensification.

Estimates from the JTWC at 0532z granted it a T5.5/102 knts, but also noted DT was T6.0/115 knts. Three hours later, a JTWC fix had a CI value of T6.0/115 knts. Additionally, a WFHC fix at 0532z went with T6.5/127 knts. A 0832Z fix from SAb went with T6.5/127 knts, with a +1.0 eye adjustment and an eye number of T5.5. Objective estimates; however, are as usual slightly higher overall. ADT present by the JTWC are at T6.5/127.5 knts, but have at 0800z a raw and adjusted value at T6.7/131 knts. JMA ADT estimates are also at T6.5/127 knts while CMISS ADT estimates are a little less bullish at T6.3/122 knts. Even though this data, when placing not nearly as much weight to the fickle ADT guidance, supported 115 knots, given the fact the eye is around in double digits and the fact that the presentation has improved since the 6z synoptic time estimate of 115 knts, but due to the above and the new fixes from JTWC and SAB, the new package is lenient and generously upgrades the intensity to 125 knts.


Maps from UW-CIMSS indicate that Nangka is approaching a region of increased vertical wind shear on the order of 15 to 25 knots courtesy of an upper-level trough to the cyclone's north and west. However, the flow around the trough becomes more divergent as it approaches Nangka, suggesting that conditions may not be quite as unfavorable as they otherwise would be. Not to mention the fact that shear has been forecast to increase for a while and right now, there are no signs of shear. Hence, the short-term forecast is as follows. Assuming shear does not cause any problems, this system is posed to attain Category 5 intensity very shortly, all that really needs to happen is the for the storm to become a bit more symmetrical. However, due to uncertainty in how legit this shear really is, 135 knts is shown at the 12 hr forecast point and Category 5 status is not blatantly forecast until 24 hours from now. Thereafter, inner core dynamics such as eyewall replacement cycles could cause for slight weakening before subsequent re-intensification and eventually the approach of an upper-level trough from the north may impart stronger shear and prompt at least temporary weakening.

Nangka is currently tracking swiftly west-northwest under the influence of a strong mid-level ridge across the northern West Pacific. This steering regime is expected to remain in place for the next 72 hours or so. Thereafter, the aforementioned upper-level trough is expected to erode the western periphery of the ridge and cause Nangka to turn more poleward at a slower rate. Both the GFS and ECMWF remain in generally good agreement throughout the forecast period, and the updated track forecast is a little faster than the old one. On its current path, Nangka is expected to pose a substantial threat to the northern and central Mariana Islands, and residents there should prepare for potentially life-threatening conditions.

INIT 07/0900Z 13.9N 153.8E 125 KT 145 MPH

12H 07/1800Z 14.4N 152.5E 135 KT 155 MPH

24H 08/0600Z 15.4N 150.3E 140 KT 160 MPH

36H 08/1800Z 16.8N 148.5E 140 KT 160 MPH

48H 09/0600Z 18.0N 146.3E 135 KT 155 MPH...NEAR NORTHERN MARIANA ISLANDS

72H 10/0600Z 19.6N 144.4E 130 KT 150 MPH

96H 11/0600Z 20.9N 142.5E 125 KT 145 MPH

120H 12/0600Z 22.9N 140.2E 120 KT 140 MPH

$$

Forecaster YE

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