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Tropical Storm Hector Discussion Number 4

Wiki-Hurricanes Forecast Center

8:00 AM PDT Wed Aug 1 2018

Hector is working out its internal core configuration this morning as it transitions from yesterday's broader curved band structure to a more rounded embedded center system. Whereas convection six hours ago was focused in a western rainband, the convective focus has now shifted to a growing central dense overcast, with the strongest rainbands occuring very close to the center as seen on microwave imagery. Some dry and subsident air appears to have mixed in with the circulation to the north as the cloud pattern there is taking on a characteristically flaky appearance on infrared channels. This is exacerbated in part by easterly wind shear which is evident in the suppression of cirrus outflow to Hector's east. CIMSS analyses a deep-layer shearing mean of just 6 kt, but it appears that there is a narrow band of unfavorable wind flow occurring at around the 400-500 mb level, which is a byproduct of a misaligned upper-level anticyclone suppressing outflow and allowing other mid- to upper-level anomalies to hinder Hector slightly. However, microwave imagery from 0957Z and 1159Z show signs of a developing mid-level eye-feature, though the supposed eyewall is not very organized. SAB and TAFB are in agreement in their estimate of T3.0/45kt for the intensity of Hector. UW-CIMSS SATCON member consensus is also at 45 kt, and given good consensus the intensity of Hector has been raised to 45 kt.

No surprises with Hector's motion this morning as it continues to pace towards the west around the southern periphery of an expansive high-pressure area now analyzed at 594 dm and centered over the Four Corners region of the United States. We are still monitoring a weak mid-level trough about 550 mi north of Hector that is allowing for some latitudinal gains, but this should taper off enough in a day's time to rebuild the ridge. Dynamical and statistical model guidance suggest that the ridge could be strong enough to force some west-southwesterly motion beginning in around 48-60 hours, with west to west-northwesterly motion resuming after that time.

Hector's progression today and development of its inner core will likely determine its future potential as it interacts with an approaching PV anomaly which could induce some unfavorable upper-level northeasterlies depending on both its orientation and proximity to Hector. Current conditions provide the warmest water and most humid air that Hector will be able to tap into, though waters should remain supportive of intensificiation or persistence throughout the entirety of the forecast period. SHIPS sees enough wind shear from the PV anomaly--at around 10-15 kt--in the next two days to curb significant strengthening; both SHIPS and LGEM see a Category 1 reaching a peak in around 96 hours. ECMWF-IFS is in general agreement with the intensity in its depiction of a minimal hurricane. GFS still shows gradual intensification out to a solid steady-state Category 2 hurricane in 120 hours. Dynamical guidance from HWRF and HMON both point to major hurricanes with more rapid intensification beginning in around 72 hours. Overall, the guidance has become more spread out, but given not much has changed environmentally, the intensity forecast at this time remains largely unchanged in its depiction of gradual strengthening in the first 48 hours followed by more appreciable gains towards 120 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 45 KT 50 MPH

12H 02/0000Z 50 KT 60 MPH

24H 02/1200Z 55 KT 65 MPH

36H 03/0000Z 60 KT 70 MPH

48H 03/1200Z 65 KT 75 MPH

72H 04/1200Z 80 KT 85 MPH

96H 05/1200Z 85 KT 100 MPH

120H 06/1200Z 90 KT 105 MPH

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