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Public advisoryEdit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 6

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST WED JUL 01 2015

...CHAN-HOM POORLY ORGANIZED...

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

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LOCATION...10.9N 159.0E

CENTER POSITION CONFIDENCE: LOW

ABOUT 260 MI...420 KM NNE OF PALIKIR, MICRONESIA

A LITTLE OVER 975 MI...1,570 KM ESE OF HAGÅTÑA, GUAM

MAXIMUM SUSTAINED WINDS...40 KT...45 MPH...75 KM/H

MINIMUM BAROMETRIC PRESSURE...1001 MB...29.56 INCHES

PRESENT MOVEMENT...W AT 12 KT...14 MPH...23 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 6:00 pm JST, the center of Tropical Storm Chan-hom was situated near 10.9N 158.3E, about 260 miles (420 km) north-northeast of Palikir, Micronesia, or a little over 975 miles (1,570 km) east-southeast of Hagåtña, Guam. Maximum sustained winds were 40 knots (45 mph, 75 km/h), with higher gusts. The minimum barometric pressure was 1001 millibars (hPa; 29.56 inHg), and the cyclone was moving swiftly west-northwestward at 14 knots (16 mph, 26 km/h). Environmental conditions are expected to favor steady to quick strengthening throughout the forecast period. On the current forecast track, Chan-hom poses a threat to the southern and central Mariana Islands, and residents there should closely monitor the progress of this cyclone.

NEXT ADVISORY

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Next complete advisory at 12:00 am JST.

$$

Forecaster YE

DiscussionEdit

TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 6

WIKI-HURRICANES FORECASTING CENTER

6:00 PM JST WED JUL 01 2015

Chan-hom is as ugly as it's name. While the mid-level circulation remains well-defined, its surface circulation has become difficult to locate. Around 20 to 30 knots of shear, slightly more than expected, continues to impede Chan-hom. This is evident if you look at the satellite photo as not only this system is sheared, it is elongated. An ASCAt pass form 2300z supports an intensity of 40-50 knts, and WindScat from earlier suggested that Chan-hom was in the 50-55 kt range with a RapidScat pass suggested an even higher estimate. However, since then, the storm's looks have fallen off the cliff. More recent CI values from the JTWC/KNES and SAB have not changed, and remain at T2.5/35 kt. A DT fix from 3z also supported T2.5/35 kt. Given the terrible presentation and irregular blob of convection, the WHFC is calling the storm a 40 knt TS, since it could have been a little stronger earlier. If the center is underneath the deep convection, which the latest ASACT hints at but does not explicitly show, then the storm is stronger than it is now, at least by a little, even though the convective mass is elongated.

In the very near term, it is possible that the center could reform to under the convection. This makes sense given the westerly flow to its south, aided by a historic Westerly Wind Burst generated by this storm as well as Raquel, and possibly some of the disturbances to its west, along with a powerful MJO pulse and CCKW.

The current structure of Chan-hom makes it clear that the upper-level setup is not ideal. As such, little intensification is expected overnight, and this system may even weaken to a tropical depression. However, water vapor animations indicate that upper-level outflow is beginning to expand in all quadrants except the east, a sign that anticyclonic flow aloft is beginning to become established, and if you ask me, Chan-hom has impressive outflow channels. This favors significant intensification in the long run. Furthermore, ocean heat and sea surface temperatures are rising, and should only help deepen the storm. The GFS brings this storm to 940 mba by day 5, which corresponds to 120-125 knts in the EPAC, so 110-115 in the WPAC when factoring in undersmapling slightly, and thus roughly the intensity listed in the forecast below, which hugs the GFS. The forecadt calls for little change in the short-term, slow intensification, and then steady to rapid at longer time frames after it builds an inner core. However, there is still some uncertainty in the intensity forecast. Many runs of the top-preforming HWRF favors a system two lows to its west, and it's still uncertain how tomorrow's consumption of the disturbance to its west will affect it in terms of intensity. In addition, Chan-hom is located in the deep tropics, and those low-lying storms can sometimes surprise people. Another althneratie is that Chan-hom degenerates into back to a trough, and later regenerates into a potent typhoon.

While the center fix is still tricky, along with the storm's percise forward speed due to the recent center formation, the cyclone is currently being steered under the influence of a 594dm mid-level ridge across the northern West Pacific, and this steering mechanism is expected to remain in place for the next 12-36 hours, while the storm remains steady state. Thereafter, global models are in good agreement that interaction with the disturbance to its southwest will cause Chan-hom to pivot southwestward. By 72 hours and beyond, an upper-level trough digging into Japan and surrounding regions is expected to erode the western periphery of the aforementioned ridge, acting to turn Chan-hom on a northwestward course. the CMC and GFS has trended a bit north north, and the spread in the model envelope has increased some, and the guidance is also in good agreement on the track philosophy. The new track is a little south of the previous and is now on the southern side of the guidance.

Chan-hom appears to be a serious threat to the central and southern Mariana Islands, and residents there should monitor the progress of the cyclone closely. Looking ahead, the GFS and its ensembles have this storm threatening Okinawa as a super typhoon late next week. Intrests in this part of the world, as well as Shanghai, where past GFS have taken this to.

INIT 01/0900Z 10.9N 158.3E 40 KT 45 MPH

12H 01/1800Z 11.4N 157.6E 40 KT 45 MPH

24H 02/0600Z 11.6N 154.2E 40 KT 45 MPH

36H 02/1800Z 11.5N 151.7E 45 KT 50 MPH

48H 03/0600Z 11.6N 149.1E 50 KT 60 MPH

72H 04/0600Z 12.7N 146.2E 65 KT 85 MPH

96H 05/0600Z 14.4N 143.9E 90 KT 105 MPH

120H 06/0600Z 17.2N 140.7E 115 KT 130 MPH

$$

Forecaster YE

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