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Hurricane Hector Discussion Number 9

Wiki-Hurricanes Forecast Center

2:00 PM PDT Thu Aug 2 2018

Despite an oncoming area of unfavorable upper-level winds, Hector has managed to avoid much considerable degradation of its inner core, and has maintained generally cold cloud tops and an eye apparent on all traditional satellite channels. Some of this resilience appears to be due to a contraction of the system's overall convective activity that has been taking place over the last few days, allowing it to build a stronger internal structure. As has been the case for much of Hector's life, a potent rainband exists in the hurricane's western semicircle, and feeds into the circulation towards the southwest. There are some indications that the increase in northeasterly shear is interfering with development in the storm's northeastern quadrant and causing for a shrinkage in the outflow-level reflection of the eyewall, but for now Hector on the overall appears to be a healthy hurricane. Microwave imagery from 1827Z shows strong core convection occuring southeast of the eye, but the eyewall remains incomplete and has not shown much progress in wrapping around the center of circulation since the morning hours. UW-CIMSS ADT indicated T4.6/80kt, while SAB estimated T5.0/90kt at 18Z, though there has been some waning of organization since then. A somewhat uncertain intensity of 85 kt is set for this advisory as a blend between the two values.

No changes to the overall track forecast as steering will continue to be driven by an expanding subtropical ridge. A west-northwesterly trajectory may begin in around 72 hours as an upper-level low currently moving into Alaska detaches from the jet stream southward into the northeastern Pacific. Ensemble guidance from EPS and GFS has shifted slightly northward with this west-northwesterly curve, and could implicate Hawaii in the future, though this is beyond the scope of the forecast window. As a general rule, the stronger the hurricane, the more readily it will drift towards steering features, i.e. northward towards the cut-off low.

Hector has managed to do well in the face of more unfavorable narrow-band upper-level winds, and it remains uncertain to what degree this will impact the system. Cirrus-demarked outflow towards the system's north shows a lack of erosion at the 250mb level, though it is certainly tricky to identify how much of an impact shear is having if the unfavorable flow has very small atmospheric thickness. Most guidance still depict a steady-state or significant weakening in the next 36 hours in anticipation of this buildup in shear, and this is very possible given the asymmetric core structure observed on microwave imagery. The current forecast continues to show a bit of a slowdown and possible decrease in strength, but is much more shallow of a drop than indicated in past advisories. After the shear abates, conditions are expected to be favorable for development, particularly between 24 and 72 hours when environmental parameters are positive across the board. Drier and more subsident conditions near Hawaii are expected to slowly dampen the system beginning in around four days.

FORECAST POSITIONS AND MAX WINDS

INIT 02/2100Z 85 KT 100 MPH

12H 03/0600Z 80 KT 90 MPH

24H 03/1800Z 85 KT 90 MPH

36H 04/0600Z 90 KT 100 MPH

48H 04/1800Z 95 KT 110 MPH

72H 05/1800Z 105 KT 120 MPH

96H 06/1800Z 100 KT 115 MPH

120H 07/1800Z 95 KT 110 MPH

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