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Hurricane Hector Discussion Number 8

Wiki-Hurricanes Forecast Center

8:00 AM PDT Thu Aug 2 2018

Hector is doing all it can this morning to build up as potent as an inner core as possible to stave off unfavorable oncoming northerly upper-level approaching from a narrow-band upper-level low to the system's east. The latest enhanced infrared images continue to show intermittent signs of an eye clearing out within the hurricane's central dense overcast. Banding is most evident towards the southwestern quadrant where outflow suppression is least evident. Equatorward outflow channels are healthy this morning, though poleward outflow is being subdued by both the potential vorticity anomaly and westerly flow from the upper-level high centered near Tijuana. SSMIS imagery from 1146Z shows a well-defined 12 mile-diameter eye surrounded by a partial eyewall spanning approximately 60% around the east and south of the center of circulation. The same eye is observed to be clearing out somewhat on this morning's first visible images. SAB estimated T4.0/65kt across the board on a curved band pattern while TAFB instead used an embedded center to derive T4.5/77kt. UW-CIMSS ADT final values have spiked this morning to a final value of T4.3/72kt. Hector is reaching a transitional stage in its infrared satellite appearance where small changes can cause large changes in estimates. A current analysis of the system based on an eye pattern feasibly yields T5.0/90kt. Based on the development of a well-defined microwave eye, the intensity for Hector is set to 75 kt this advisory, which could be conservative.

Expansive 591 dm ridging over the southwestern United States and northwestern Mexico is keeping a westerly course this morning. Over the next two days, this ridge should extend westward and strengthen, which should induce a slight bearing south of west beginning in around 48 hours. A mid-level low currently over the Bering Sea is expected drift into the northeastern Pacific and become cut off from the jet stream in around four days, weakening the ridge enough to either allow resumption of westerly movement by 120 hours or result in slight motion north of west. Within the forecast window, statistical and dynamical guidance are in general consensus over this track philosophy.

With the eye beginning to emerge on shortwave infrared and visible channels, Hector continues to rapidly intensify. The big question mark is how Hector will deal with an approaching area of northeasterly upper-level winds creating a 15-20kt wind shear locality northeast of Hector. The boundary of this area is denoted on water vapor channels as a contrast between Hector's local outflow bubble and subsident subtropical air, and has reached Hector's rainbands. It remains to be seen how the core and the storm as a whole handles this shear, though models generally either maintain Hector's intensity or weaken it over the next 36 hours or so with the exception of statistical guidance from SHIPS and LGEM. Dynamical guidance has been the most accurate in assessing Hector's rapid intensification this morning but are also the most dramatic in seeing Hector weaken considerably this afternoon, assessing a drop to a low-end or mid-tier tropical storm. Conditions should improve after 36 hours as shear abates, allowing for strengthening thereafter. Conditions late in the forecast run are characteristic of conditions which have allowed for the development of annular tropical cyclones in the past, so even despite drying conditions at the end of the forecast period, Hector could maintain its intensity better than it ordinarily would. The current intensity forecast carries the same general philosophy as the last advisory but has been adjusted somewhat based on current assessment of environmental conditions.

FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 75 KT 85 MPH

12H 03/0000Z 65 KT 75 MPH

24H 03/1200Z 55 KT 65 MPH

36H 04/0000Z 65 KT 75 MPH

48H 04/1200Z 75 KT 85 MPH

72H 05/1200Z 90 KT 105 MPH

96H 06/1200Z 105 KT 120 MPH

120H 07/1200Z 100 KT 115 MPH

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