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Tropical Storm Hector Discussion Number 47

Wiki-Hurricanes Forecast Center

5:00 AM HST Sun Aug 13 2018

Hector is taking a massive beating from strong channelized wind shear this morning caused by a nearby upper-level low to the cyclone's west, placing the circulation of Hector across a steep deep-layer wind shear gradient that has the storm within 15-40 kt of wind shear across different points across Hector. The end result has been the complete extrication of convective activity from the low-level circulation, which began around the time of the last advisory and has since decayed, with disorganized pop-up showers taking the place of the old central dense overcast. PHFO, PGTW, and SAB were all consensus T3.0/45kt for current intensities at 12z, while UW-CIMSS ADT has already sunken to T1.6/26kt. A 0934z ASCAT scatterometer pass missed the eastern half of Hector but showed that the western hemisphere only featured peak winds of around 30-35 kt in the northwestern quadrant, though the circulation remains well-defined. An older 0827z pass recorded the entire circulation of Hector and verified that the strongest winds of the tropical storm were located in the northeastern quadrant unseen by ASCAT, but perhaps due to its comparatively lower resolution only sampled maximum 30-35 kt winds. A blend between scatterometer data and satellite estimates would suggest a 40 kt intensity for this advisory.

While Hector is facing exceptional shear across its circulation, the associated upper-level low-to-blame should begin positioning itself away further from Hector, allowing shear to lessen. SHIPS diagnostic parameters do not take into account shear not directly over the model's estimate of the storm's center position, but it does indeed drop shear off to very low values later today as an upper-level anticyclone becomes more favorable placed to counteract the shear. During this time sea surface temperatures are supportive for storm development and should stay that way for about the next three or so days. The main concern for Hector is marginal to dry conditions, which are problematic for a storm like Hector where the center is already exposed and convective activity is already limited. It may find current conditions more difficult to withstand than the dry conditions it faced while an annular major hurricane near Hawaii. Water vapor imagery already shows the upper-level low whipping up dry air into Hector's circulation from the south, and this may seek to limit reintensification as shown by some of the model guidance.

SHIPS and LGEM restrengthen Hector to a moderate tropical storm in about two days before petering out, as does dynamical guidance from HWRF and HMON. GFS is the most agressive global synoptic model, and still only features a strong tropical storm while other globals show steady state or gradual weakening in the next three days. The current forecast still carries the reintensification potential, but now only to 50 kt, before increased shear and cooler waters kills the system off in around five days.

Hector is traveling towards the west to west-northwest this morning as it is guided by an elongated 594 dm subtropical ridge that extends all the way from the Korean Peninsula and eastern China to the Yukon. The approach of a shortwave trough that will emerge off Primorsky Krai in around two days should allow Hector to find a western periphery to the ridge and curve towards the north and then start bending east by the end of the forecast window. The same upper-level low sharing Hector right now should provide an additional weakness in this ridge to allow Hector to make this turn earlier than what would typically be expected. Model guidance is in very good agreement over this scenario and the precise track of Hector.

The latest satellte images show that the center of circulation of Hector has crossed the International Date Line, and did so at around 14z. As it is exiting our area of responsibility, this will be the last advisory from WHFC on Hector. It has been fun tracking this resilient and tenacious tropical cyclone for two weeks, and it remains in an elite class of triple basin crossers. This will also be my last advisory for WHFC... so cheers and sayonara!

MAXIMUM WINDS FORECAST

INIT 13/1500Z 40 KT 45 MPH...ENTERED WEST PACIFIC

12H 14/0000Z 40 KT 50 MPH

24H 14/1200Z 45 KT 50 MPH

36H 15/0000Z 50 KT 60 MPH

48H 15/1200Z 50 KT 60 MPH

72H 16/1200Z 45 KT 50 MPH

96H 17/1200Z 40 KT 45 MPH

120H 18/1200Z 30 KT 35 MPH...POST-TROP/REMNT LOW