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Hurricane Hector Forecast Discussion Number 19

2018-08-05 10:51:16| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Aug 05 2018 218 WTPZ45 KNHC 050851 TCDEP5 Hurricane Hector Discussion Number 19 NWS National Hurricane Center Miami FL EP102018 200 AM PDT Sun Aug 05 2018 Hector has maintained a well-defined, 10-nmi-diameter eye inside a gradually shrinking central dense overcast. Satellite intensity estimates at 0600Z from TAFB and SAB supported an intensity of 102 kt, while UW-CIMSS ADT raw estimates have been near 100 kt. However, more recent infrared satellite images indicate intensity estimates just below 115 kt, so the advisory intensity of 110 kt is based on a blend of the available estimates with more weight placed on recent IR trends. The initial motion remains 275/10 kt. A large, deep-layer ridge to the north of Hector is expected to steer the hurricane westward for the next 24 h or so, followed by a modest poleward 'stair-step' in the track through 72 h due to a dissipating frontal trough pushing southward and becoming stationary northeast of the Hawaiian Islands, which should weaken the low-level ridge. After that time, however, the surface trough is forecast to weaken, allowing the ridge to build back across the Islands, forcing Hector back onto a more westerly course on days 4 and 5. More weakening of the ridge in 48-72 hours has resulted in yet another northward shift in the guidance envelope, with the HWRF and HMON models bringing Hector within 60 nmi of the Big Island on day 4. The new NHC forecast track has been shifted slightly northward as a result, but lies just a tad south of the consensus models out of respect for the reliable ECMWF model, which is the southernmost of all of the global and regional models. Outer banding features have become less evident since the previous advisory, and with Hector moving into an increasingly drier airmass, the chances of Hector evolving into an annular hurricane are increasing in the longer term. Although the hurricane will be embedded within a light vertical wind shear environment, marginal SSTs and a much drier airmass characterized by mid-level humidity values less than 40 percent are expected to produce a slow weakening trend throughout the forecast period. The official intensity forecast is a little lower than the previous advisory, and closely follows the intensity consensus models HCCA, FSSE, and IVCN, which all show steady weakening. While the official forecast track continues to lie south of the Hawaiian Islands, it is too soon to determine what kind of impacts might occur in the state, since track errors can be large at long time ranges. This remains a good time for everyone in the Hawaiian Islands to ensure they have their hurricane plan in place. For additional information on any potential local impacts from Hector in Hawaii, please refer to products issued by the NWS Weather Forecast Office in Honolulu at http://www.prh.noaa.gov/hnl . FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 14.4N 135.7W 110 KT 125 MPH 12H 05/1800Z 14.6N 137.5W 110 KT 125 MPH 24H 06/0600Z 15.0N 139.9W 105 KT 120 MPH 36H 06/1800Z 15.6N 142.7W 105 KT 120 MPH 48H 07/0600Z 16.2N 145.6W 100 KT 115 MPH 72H 08/0600Z 16.9N 151.8W 95 KT 110 MPH 96H 09/0600Z 17.2N 157.4W 90 KT 105 MPH 120H 10/0600Z 17.7N 162.6W 85 KT 100 MPH $$ Forecaster Stewart

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Tropical Depression Eleven-E Forecast Discussion Number 3

2018-08-05 10:50:46| National Hurricane Center (East Pacific)

Issued at 400 AM CDT Sun Aug 05 2018 832 WTPZ41 KNHC 050850 TCDEP1 Tropical Depression Eleven-E Discussion Number 3 NWS National Hurricane Center Miami FL EP112018 400 AM CDT Sun Aug 05 2018 Convection associated with the depression has increased through the early morning, but the system still appears to be sheared from the north. A pair of ASCAT passes between 03Z and 04Z revealed that the center of the depression is elongated and has reformed to the south, closer to the convection. The maximum believable winds in the ASCAT data were around 30 kt, and the initial intensity has been set at that value. Little change has been made to the track or intensity forecast, however confidence is low. The global and regional dynamical models all forecast that a disturbance to the west will develop later today and quickly become the dominant cyclone. This should cause the depression to dissipate as it becomes entangled in the other system's larger circulation. However, there is little agreement among the models as to when or where this will occur. On one hand, the GFS continues to insist that the depression will dissipate later this morning, while the UKMET shows two distinct cyclones through 96 hours. Further complicating matters, the close proximity of the two cyclones is affecting the trackers used to obtain track and intensity information from the dynamical models, and most of the dynamical tracker output can not be considered representative, especially at 48 h and beyond. Assuming the depression persists for at least a couple more days, the ECMWF and HWRF models appear to be the best compromise solutions, with both showing the depression accelerating northwestward between the disturbance to the west and a mid-level ridge to the east, before dissipating in 48-72 h. The NHC track forecast therefore leans most heavily on a blend of these models and the previous forecast track. The intensity forecast is based primarily on the statistical models, since the dynamical tracker output appears to be unrepresentative of the actual forecasts. Although the official forecast conservatively maintains the depression for 72 h, the cyclone could dissipate much sooner than currently indicated. Based on the forecast, any tropical-storm-force winds are expected to remain offshore the coast of Mexico. However, given the low confidence in both the track and intensity of the depression, interests along the southern and southwestern coast of Mexico should monitor its progress in case the track shifts closer to the coast or the cyclone strengthens and grows larger than forecast. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 13.0N 96.9W 30 KT 35 MPH 12H 05/1800Z 13.5N 98.5W 35 KT 40 MPH 24H 06/0600Z 14.6N 100.5W 35 KT 40 MPH 36H 06/1800Z 16.0N 103.1W 40 KT 45 MPH 48H 07/0600Z 17.5N 105.8W 45 KT 50 MPH 72H 08/0600Z 20.0N 111.4W 40 KT 45 MPH 96H 09/0600Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Hector Forecast Discussion Number 18

2018-08-05 04:39:42| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Aug 04 2018 058 WTPZ45 KNHC 050239 TCDEP5 Hurricane Hector Discussion Number 18 NWS National Hurricane Center Miami FL EP102018 800 PM PDT Sat Aug 04 2018 Hector has the textbook appearance of a major hurricane in satellite imagery this evening, as it is maintaining a well-defined 10 nm wide eye inside a central dense overcast. Satellite intensity estimates are mostly near 115 kt, and based on these estimates that will be the initial intensity for this advisory. The most notable change since the last advisory has been an increase in convection in an outer band that now mostly surrounds the CDO. The initial motion is 275/10. There is little change to the forecast philosophy from the previous advisory. A large subtropical ridge to the north should steer the hurricane generally westward through the forecast period, with Hector gradually gaining some latitude on Sunday and beyond due to a weakness in the ridge. By 72-96 h, most of the guidance shows a more westward motion south of the Hawaiian Islands. Based on slight shifts in the consensus models, the new forecast track is nudged a little to the north of the previous track through 72 h, and it is similar to the previous track after that time. It should be noted that there remains some spread in the dynamical models as Hector approaches Hawaii, with the NAVGEM, HWRF, and GFS to the north of the center of the guidance envelope and the ECMWF to the south. The recent increase in outer band convection decreases the short- term chance that Hector will become an annular hurricane. However, the cyclone will be in the light-shear moderate-SST conditions favorable for such an evolution, and it could occur later in the forecast period. Before this, it is likely that Hector will undergo another eyewall replacement with associated fluctuations in intensity. After 36-48 h, the hurricane should start to encounter a drier airmass and slowly weaken in consequence. The new NHC intensity forecast is unchanged from the previous one, and it lies at the upper end of the intensity guidance. While the official forecast track continues to lie south of the Hawaiian Islands, it is too soon to determine what kind of impacts might occur in the state, since track errors can be large at long time ranges. This remains a good time for everyone in the Hawaiian Islands to ensure they have their hurricane plan in place. For additional information on any potential local impacts from Hector in Hawaii, please refer to products issued by the NWS Weather Forecast Office in Honolulu at http://www.prh.noaa.gov/hnl . FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 14.3N 134.7W 115 KT 130 MPH 12H 05/1200Z 14.5N 136.3W 115 KT 130 MPH 24H 06/0000Z 14.8N 138.7W 115 KT 130 MPH 36H 06/1200Z 15.3N 141.3W 115 KT 130 MPH 48H 07/0000Z 15.8N 144.2W 110 KT 125 MPH 72H 08/0000Z 16.5N 150.5W 100 KT 115 MPH 96H 09/0000Z 17.0N 156.0W 90 KT 105 MPH 120H 10/0000Z 17.5N 161.5W 85 KT 100 MPH $$ Forecaster Beven

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Tropical Depression Eleven-E Forecast Discussion Number 2

2018-08-05 04:38:14| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Sat Aug 04 2018 203 WTPZ41 KNHC 050238 TCDEP1 Tropical Depression Eleven-E Discussion Number 2 NWS National Hurricane Center Miami FL EP112018 1000 PM CDT Sat Aug 04 2018 After having a somewhat impressive satellite presentation earlier today, the final GOES-16 visible images showed what appeared to be the cyclone's low-level center popping out from the northwestern edge of the convective canopy. Since that time, the remaining convection south and east of the center has become less organized, apparently due to enhanced wind shear associated with a linear band of convection to the northwest of the cyclone. This structural degradation of the system further complicates what was already a low-confidence forecast due to the depression interacting with the developing system located to its west. The 18Z GFS doesn't have much of a representation of the depression, and it is quickly lost in the model integration. The latest HWRF fields show the vortex being absorbed into the circulation of the disturbance to the west after 24 hours, and the HMON shows the system dissipating in 2 to 3 days. On the other hand, the 12Z runs of the ECMWF and UKMET maintain the depression into days 4 and 5, respectively. In an effort to maintain some continuity with the previous forecast while acknowledging the current trends, the new intensity forecast still shows some strengthening but at a slower rate given that the upper-level winds appear to be winning out so far over the warm SSTs. The official forecast carries the tropical cyclone through 72 hours with dissipation shown at day 4, but it would not be surprising if the cyclone dissipated much sooner than indicated here. The initial motion estimate is a somewhat more confident 295/10 given that the center was exposed right around 00Z. The track forecast reasoning has not changed, as the small cyclone should be steered west-northwestward by a large ridge to its north and the aforementioned disturbance to the west, which the model guidance suggests will strengthen quickly during the next couple of days. The new NHC forecast is a bit to the right of the previous one and is close to a blend of the ECMWF and UKMET models. Based on the forecast, any tropical-storm-force winds are expected to remain offshore the coast of Mexico. However, given the low confidence in both the track and intensity of the depression, interests along the southern and southwestern coast of Mexico should monitor its progress in case the track shifts closer to the coast or the cyclone strengthens and grows larger than forecast. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 13.0N 95.9W 25 KT 30 MPH 12H 05/1200Z 13.4N 97.3W 25 KT 30 MPH 24H 06/0000Z 14.2N 99.4W 30 KT 35 MPH 36H 06/1200Z 15.1N 101.5W 35 KT 40 MPH 48H 07/0000Z 16.3N 103.8W 40 KT 45 MPH 72H 08/0000Z 19.0N 109.5W 40 KT 45 MPH 96H 09/0000Z...DISSIPATED $$ Forecaster Brennan

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Hurricane Hector Forecast Discussion Number 17

2018-08-04 22:44:10| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Aug 04 2018 558 WTPZ45 KNHC 042044 TCDEP5 Hurricane Hector Discussion Number 17 NWS National Hurricane Center Miami FL EP102018 200 PM PDT Sat Aug 04 2018 Satellite images indicate that the small eye of Hector has grown larger over the past several hours, with a rapid axisymmetrization of the eyewall convection. It seems that the eyewall cycle has completed itself rather quickly, with one distinct eyewall now noted. Dvorak estimates are on the rise again, and the latest initial wind speed is set to 110 kt, which is a blend of the latest satellite estimates. While there has been no scatterometer data during the past day or so, the microwave data show that Hector has grown in size, so the initial wind radii have been expanded, although are smaller than the latest CIMSS and CSU/CIRA estimates. Hector appears to be in the process of becoming an annular hurricane, with little outer banding and a fairly symmetric inner core. This subset of hurricanes is known to occur under moderate SSTs below 28.5C, with light easterly shear and no trough interactions. The bottom line for the intensity forecast is that these conditions are likely to persist near Hector for the next few days, and intensity guidance is known to have a low bias for annular hurricanes. The new intensity forecast is raised from the previous one, and is near or above the guidance, showing only a slow demise over the central Pacific as environmental conditions gradually deteriorate. Hector continues a westward motion of 270/10 kt. A large subtropical ridge to the north should steer the hurricane generally westward throughout the forecast period, with Hector gradually gaining some latitude on Sunday and beyond due to a weakness in the ridge. By 96 hours, most of the guidance shows a more due-westward motion south of the Hawaiian Islands. The only significant change from the past advisory is a slightly slower forward speed for the first couple of days. While the official forecast track continues to lie south of the Hawaiian Islands, it is too soon to determine what kind of impacts might occur in the state, since track errors can be large at long range. This remains a good time for everyone in the Hawaiian Islands to ensure they have their hurricane plan in place. For additional information on any potential local impacts from Hector in Hawaii, please refer to products issued by the NWS Weather Forecast Office in Honolulu at http://www.prh.noaa.gov/hnl . FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 14.2N 133.7W 110 KT 125 MPH 12H 05/0600Z 14.3N 135.2W 115 KT 130 MPH 24H 05/1800Z 14.5N 137.4W 115 KT 130 MPH 36H 06/0600Z 14.8N 139.9W 115 KT 130 MPH 48H 06/1800Z 15.3N 142.7W 110 KT 125 MPH 72H 07/1800Z 16.3N 148.7W 100 KT 115 MPH 96H 08/1800Z 16.7N 154.5W 90 KT 105 MPH 120H 09/1800Z 17.0N 160.0W 85 KT 100 MPH $$ Forecaster Blake

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