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Hurricane DARBY Forecast Discussion Number 30

2016-07-19 04:31:55| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON JUL 18 2016 000 WTPZ45 KNHC 190231 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 30 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 PM PDT MON JUL 18 2016 Darby still appears as a well-organized tropical cyclone on geostationary imagery, with a symmetric CDO and occasional eye showing up on enhanced infrared imagery. Microwave imagery, however, shows that the system has a slight northward tilt with height with the mid-level center located a few tenths of a degree north of the low-level center. Dvorak classifications from SAB and TAFB still support hurricane strength, so the official intensity estimate remains at 65 kt. Darby will be moving over marginal SSTs and into drier air with increasing shear during the next several days. Therefore, the cyclone is forecast to gradually weaken during the forecast period. The official forecast is a blend of the latest SHIPS and LGEM model output through 72 hours and is a little above that guidance at days 4 and 5. Based on the microwave images, the center is positioned slightly south of the fixes from GOES imagery, and the resulting motion estimate is 280/11 kt. The track forecast reasoning is about the same as in the previous advisory. Darby should continue on a generally westward heading to the south of a zonally-oriented mid-level subtropical ridge for the next couple of days. Later in the period, the cyclone should slow its forward speed as it nears a weakness in the ridge. The official track forecast lies roughly in the middle of the dynamical guidance. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 19.1N 133.2W 65 KT 75 MPH 12H 19/1200Z 19.6N 134.9W 60 KT 70 MPH 24H 20/0000Z 20.0N 136.9W 55 KT 65 MPH 36H 20/1200Z 20.1N 139.1W 50 KT 60 MPH 48H 21/0000Z 19.9N 141.3W 45 KT 50 MPH 72H 22/0000Z 19.5N 145.5W 35 KT 40 MPH 96H 23/0000Z 19.0N 150.0W 35 KT 40 MPH 120H 24/0000Z 20.0N 152.5W 30 KT 35 MPH $$ Forecaster Pasch

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Tropical Storm ESTELLE Forecast Discussion Number 14

2016-07-18 22:36:39| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON JUL 18 2016 000 WTPZ41 KNHC 182036 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 200 PM PDT MON JUL 18 2016 Banding features associated with Estelle have become a little better defined this afternoon, but the tropical storm still lacks an inner core. In fact, this afternoon's ASCAT data continues to show a large radius of maximum winds. Satellite classifications from TAFB, SAB, and UW/CIMSS have not changed much during the past 24 hours, so the initial wind speed will remain 60 kt for this advisory. Estelle's refusal to intensify has likely been the result of shear and intrusions of dry mid-level air. Since the shear appears to have decreased and the tropical storm is predicted to remain over warm water for another 36-48 h, one would think that Estelle should be able to strengthen and finally attain hurricane status. However, this will likely be dependent on the cyclone consolidating inner-core convection, which is nearly impossible to forecast. It may sound like a broken record, but the NHC forecast once again calls for Estelle to become a hurricane during the next 12 to 24 hours. After 36 h, gradually decreasing SSTs and a less favorable thermodynamic environment should cause weakening. A faster rate of reduction in wind speed should occur later in the forecast period when the cyclone moves over SSTs below 24C, and Estelle is predicted to become post-tropical on day 4. Recent fixes indicate that Estelle continues to move west- northwestward. The track forecast philosophy remains unchanged from the previous advisory. Estelle should continue west-northwestward for the next several days, then turn northwestward late in the forecast period, into a weakness in the subtropical ridge. The track guidance continues to be tightly clustered and the NHC forecast lies between the typically better performing global models. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 17.8N 115.8W 60 KT 70 MPH 12H 19/0600Z 18.3N 117.2W 65 KT 75 MPH 24H 19/1800Z 18.8N 119.1W 70 KT 80 MPH 36H 20/0600Z 19.2N 121.4W 70 KT 80 MPH 48H 20/1800Z 19.7N 123.8W 60 KT 70 MPH 72H 21/1800Z 21.2N 129.0W 45 KT 50 MPH 96H 22/1800Z 24.0N 134.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 23/1800Z 28.0N 137.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm ESTELLE Forecast Discussion Number 13

2016-07-18 16:50:21| National Hurricane Center (East Pacific)

Issued at 900 AM MDT MON JUL 18 2016 000 WTPZ41 KNHC 181450 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 900 AM MDT MON JUL 18 2016 Although the cloud tops are not as cold as they were yesterday, the area of convection is a little more symmetric around the center indicating that the northwesterly shear is relaxing. A couple of recent microwave images also show less tilt between the low- and mid-level centers, however the inner core is still not well organized. The initial wind speed is maintained at 60 kt, which is a little above the latest Dvorak estimates. An automated weather station on Clarion Island, about 35 n mi north of the center, recently reported a sustained wind of 51 kt with a gust to 71 kt. The vertical wind shear over Estelle is forecast to become very low later today, and remain light during the next few days. Since the tropical storm is forecast to remain over warm water for another 36 hours or so, modest strengthening is still anticipated and the NHC forecast and most of the guidance still calls for Estelle to become a hurricane within the next 24 hours. In 36 to 48 h, the cyclone will be moving over decreasing SSTs which should commence the weakening process. A faster rate of weakening should begin by 72 hours, when Estelle moves over SSTs below 24C and into a more stable airmass. The initial motion estimate is 295/9 kt. Estelle should move west-northwestward to the south of the subtropical ridge during the next 3 to 4 days. After that time, a weakness in the ridge caused by a mid- to upper-low to the northeast of the Hawaiian Island should cause the cyclone to turn northwestward by day 5. The track guidance is in good agreement, but most of the typically better performing models are along the northern side of the guidance envelope. As a result, the NHC track forecast is a little north of the multi-model consensus and is near a blend of the GFS, ECMWF, and UKMET models. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 17.7N 114.9W 60 KT 70 MPH 12H 19/0000Z 18.2N 116.3W 65 KT 75 MPH 24H 19/1200Z 18.7N 118.2W 70 KT 80 MPH 36H 20/0000Z 19.1N 120.2W 75 KT 85 MPH 48H 20/1200Z 19.5N 122.5W 70 KT 80 MPH 72H 21/1200Z 20.9N 127.5W 50 KT 60 MPH 96H 22/1200Z 23.5N 132.5W 35 KT 40 MPH 120H 23/1200Z 27.5N 136.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Hurricane DARBY Forecast Discussion Number 28

2016-07-18 16:43:19| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON JUL 18 2016 000 WTPZ45 KNHC 181443 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 AM PDT MON JUL 18 2016 Deep convection associated with Darby continues to diminish this morning with a couple of thin, fragmented curved bands located just to the southwest of the center of circulation. The initial intensity is, therefore, lowered to 65 kt and agrees with a blend of the subjective and objective satellite intensity estimates. The cyclone is currently moving over SSTs near 24C, but will soon be traversing slightly warmer water during the next day or two. Consequently, there could be some convective banding redevelopment which could temporarily curtail weakening. After that time, the global models all indicate an increase in westerly shear which is expected to influence further weakening through the end of the period. The NHC intensity forecast reflects gradual weakening and is slightly above the Decay SHIPS and LGEM models. The initial motion estimate is 280/9 kt, to the south of a narrow mid-tropospheric ridge extending along 30N. A generally westward to west-northwestward motion with a slight increase in forward speed is forecast during the next 72 hours. Through the remaining portion of the forecast period, the aforementioned ridge is expected to briefly strengthen, causing the cyclone to move just a bit south of due west. The official forecast is again shifted a little northward and is located between the multi-model consensus and a blend of the GFS and ECMWF ensemble mean guidance. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 18.7N 131.1W 65 KT 75 MPH 12H 19/0000Z 19.1N 132.8W 55 KT 65 MPH 24H 19/1200Z 19.7N 135.0W 50 KT 60 MPH 36H 20/0000Z 20.1N 137.3W 45 KT 50 MPH 48H 20/1200Z 20.2N 139.6W 40 KT 45 MPH 72H 21/1200Z 19.6N 144.3W 35 KT 40 MPH 96H 22/1200Z 18.7N 149.0W 35 KT 40 MPH 120H 23/1200Z 18.8N 152.1W 30 KT 35 MPH $$ Forecaster Roberts

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Hurricane DARBY Forecast Discussion Number 27

2016-07-18 10:50:16| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON JUL 18 2016 000 WTPZ45 KNHC 180850 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 27 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 AM PDT MON JUL 18 2016 Stable air and cool SSTs are taking a toll on Darby. Although the system still has a well organized circulation and eye feature, deep convection has been on a steady decline since the previous advisory. In fact, the cloud tops are now warmer than -50 deg C. The initial wind speed is lowered to 70 kt, based on a blend of the Final T- and CI-numbers from TAFB and SAB. Cool water and dry air should continue to affect Darby during the next few days, which will likely result in continued weakening. Beyond that time, SSTs are expected to increase along the forecast track, but the cyclone will also be moving into an environment of increasing westerly shear. Given these mixed signals, little change in strength is shown at the end of the forecast period. The NHC intensity forecast is largely an update of the previous one and is close to the intensity model consensus. Darby is moving a 275/09 kt, and is being steered by a narrow mid-level ridge to its north. A westward to west-northwestward motion at a slightly faster pace is forecast during the 2 to 3 days while the ridge remains in place. After that time, a motion slightly south of due west is predicted when a mid-level high builds to the northwest of the tropical cyclone. The latest guidance has shifted a little to the north this cycle, and the NHC official track forecast has been nudged in that direction. Based on this forecast, a much weaker Darby could be approaching the Hawaiian Islands at the end of the period. An ASCAT-B pass around 0615 UTC was helpful in estimating the wind radii of Darby. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 18.5N 130.2W 70 KT 80 MPH 12H 18/1800Z 18.8N 131.8W 60 KT 70 MPH 24H 19/0600Z 19.3N 134.1W 55 KT 65 MPH 36H 19/1800Z 19.8N 136.4W 50 KT 60 MPH 48H 20/0600Z 20.0N 138.7W 45 KT 50 MPH 72H 21/0600Z 19.6N 143.2W 40 KT 45 MPH 96H 22/0600Z 18.6N 148.0W 35 KT 40 MPH 120H 23/0600Z 18.3N 151.8W 35 KT 40 MPH $$ Forecaster Cangialosi

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