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Hurricane Hector Discussion Number 17

Wiki-Hurricanes Forecast Center

8:00 PM PDT Sat Aug 4 2018

Hurricane Hector has maintained a strong intensity throughout the day, which is likely a result of marginal conditions supportive of intensity maintenance and the storm's partially annular characteristics from earlier this morning and afternoon. However, since that time, Hector internally has transitioned from a more annular circulation to a traditional cyclone, with microwave imagery from 0013Z showing several strong spiral bands wrapping inward from the southwest and northwest, with the tendrils of weaker bands developing from the east. These changes do not necessarily confer a lower or higher intensity, and the system in general appears as well organized as it did earlier, and not much appears to have changed on infrared imagery, with the only changes appearing to be in line with oceanic diurnal variation. TAFB estimated T5.5/102kt at 00z, while SAB maintained its higher estimate from this afternoon of T6.0/115kt. UW-CIMSS ADT is holding steady at T6.0/115kt, with very similar SATCON values of 118 kt. With no convincing reason to change values, 115 kt remains Hector's current intensity.

Hector has been cruising west in the easterly flow on the southern end of subtropical ridging, but a slight uptick in latitudes could begin tonight as it begins a long anticipated west-northwesterly curve. An expansive extratropical cyclone over the far northeastern Pacific roughly level with the contiguous US-Canada border is beginning to make its influence known on the subtropical ridge, and is beginning to carve a slight weakness which will be responsible for the slight west-northwestward drift. Very much akin to a squeezed toothpaste tube, however, the compression of the ridge should result in a lob of the ridge separating and taking residence north of Hawaii, inducing a westward curve in around 72 hours. The most likely scenario for Hector is a westerly track that brings it 100 miles south of Hawaii's Big Island, but given the spread in the guidance this afternoon a landfall on the islands cannot be ruled out.

Atmospheric conditions ahead of Hector for the next five days or so are favorable for "cruise control"—that is, they straddle the line between favorable and unfavorable and only gradually worsen over time, allowing Hector to either very slowly taper off during the forecast period. While conditions are not necessarily favorable within the next day or two, a lack of unfavorable winds could give the hurricane the opportunity to marginally strengthen during that time, and some minor intensification continues to be depicted in the intensity forecast and by global synoptic and dynamical hurricane guidance. Conditions remain in place for annular structural development and persistence within the forecast window as upper-level winds are expected to facilitate a sandbox like environment for Hector to refine its circulation. After two days, the overall environment should become rather dry and subsident, and it will be up to Hector and its organization to maintain a moisture bubble for itself on its westward trek, though inevitably the subsiednt enivronment will shallow out convection some and dampen Hector's intensity as it approaches Hawaii. After its closest approach to Hawaii in around 96-120 hours, the storm's intensity will be largely dependent on how close it nears the islands. A trek closer to the Big Island and its twin shield volcanoes could bring the storm in highly hostile downslope flow which would weaken the storm considerably. A track south could renew Hector in a fresh batch of favorable conditions which would jumpstart reintensification at 96 hours. As ensemble guidance has not changed considerably in their depiction of Hector's overall nearness to the islands, the forecast for this advisory remains largely unchanged from the last advisory.

FORECAST POSITIONS AND MAX WINDS

INIT 05/0300Z 115 KT 130 MPH

12H 05/1200Z 120 KT 140 MPH

24H 06/0000Z 120 KT 140 MPH

36H 06/1200Z 120 KT 140 MPH

48H 07/0000Z 110 KT 120 MPH

72H 08/0000Z 100 KT 115 MPH

96H 09/0000Z 95 KT 100 MPH ...CLOSEST APPROACH TO HAWAII

120H 10/0000Z 95 KT 100 MPH