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Hurricane DARBY Forecast Discussion Number 20

2016-07-16 16:47:40| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SAT JUL 16 2016 000 WTPZ45 KNHC 161447 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 AM PDT SAT JUL 16 2016 Darby continues to have a well-defined 20 n mi wide eye, which is completely encircled by convective cloud tops as cold as -70C. Satellite intensity estimates at 1200 UTC were rather conflicting. Subjective Dvorak numbers increased from six hours ago, but at the same time objective ADT estimates have decreased. Given this discrepancy, the initial intensity is kept at 90 kt. Darby is beginning to move over cooler water, with the eye having reached the 26C isotherm. Although vertical shear over the cyclone is expected to be low for the next few days, SSTs will be dropping to as cold as 23C by 72 hours. Therefore, gradual weakening is anticipated to begin soon, with Darby likely becoming a tropical storm in about 48 hours. Increasing shear should then contribute to a faster weakening rate after 48 hours. The new NHC intensity forecast is very close to the IVCN intensity consensus during the entire forecast period, and it is a little lower than the previous forecast from 36 hours and beyond. The initial motion is west-northwestward, or 290/9 kt. The subtropical ridge to the north of Darby is in the process of weakening due to an amplifying trough along the west coast of the United States. Therefore, Darby is expected to continue moving west-northwestward for the next 24 hours. After that time, the weakening cyclone will come under the influence of lower-level steering, causing it to move westward through the end of the forecast period. There is very little spread among the track models, and the NHC track forecast is just an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 17.8N 123.9W 90 KT 105 MPH 12H 17/0000Z 18.2N 125.1W 85 KT 100 MPH 24H 17/1200Z 18.6N 126.8W 75 KT 85 MPH 36H 18/0000Z 18.9N 128.7W 65 KT 75 MPH 48H 18/1200Z 19.1N 130.7W 60 KT 70 MPH 72H 19/1200Z 19.7N 135.2W 50 KT 60 MPH 96H 20/1200Z 19.9N 140.0W 40 KT 45 MPH 120H 21/1200Z 19.0N 145.0W 35 KT 40 MPH $$ Forecaster Berg

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Tropical Storm ESTELLE Forecast Discussion Number 5

2016-07-16 16:47:08| National Hurricane Center (East Pacific)

Issued at 900 AM MDT SAT JUL 16 2016 000 WTPZ41 KNHC 161446 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 900 AM MDT SAT JUL 16 2016 Convective banding associated with Estelle continues to increase and become better organized, with a large band wrapping around the southwestern portion of the circulation, and broken bands of convection to the east and southeast of the center. Recent microwave and early-light visible satellite pictures indicate that the center of the tropical cyclone is located northeast of the earlier estimates, which required some relocation of Estelle for this advisory. With the increase in organization, Dvorak T-numbers have responded accordingly, and support raising the initial intensity to 45 kt. Estelle is forecast to remain in a moist and low wind shear environment during the next several days. These conditions, along with warm water along the forecast track, should allow for strengthening, and Estelle is forecast to become a hurricane in a day or so. After that time, the track forecast takes the cyclone just north of the cold wake left behind by previous hurricanes, and continued intensification is likely. After 72 hours, the tropical cyclone is forecast to move over cooler waters which should induce gradual weakening. The NHC intensity forecast is a blend of the various intensity models, and shows a peak intensity slightly higher than the SHIPS/LGEM guidance. Due to the relocation of the center, the initial motion estimate is a somewhat uncertain 290/7 kt, which is slightly slower than before. Estelle is expected to continue moving west-northwestward during the next few days to the south of a mid-level ridge that extends westward from northern Mexico. After that time, there is increasing spread in the guidance due to differences in the strength of the ridge. The GFS depicts a weaker ridge after 72 hours due to a developing trough off the west coast of the United States and takes the tropical cyclone west-northwestward to northwestward near the end of the forecast period. The ECMWF is on the southern side of the guidance envelope as it maintains more ridging and takes Estelle more westward. The updated NHC track lies between these solutions and is close to the Florida State Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 15.7N 109.0W 45 KT 50 MPH 12H 17/0000Z 16.0N 110.0W 55 KT 65 MPH 24H 17/1200Z 16.4N 111.4W 60 KT 70 MPH 36H 18/0000Z 16.8N 112.9W 65 KT 75 MPH 48H 18/1200Z 17.2N 114.5W 75 KT 85 MPH 72H 19/1200Z 18.1N 117.8W 85 KT 100 MPH 96H 20/1200Z 18.5N 121.8W 80 KT 90 MPH 120H 21/1200Z 19.5N 126.5W 65 KT 75 MPH $$ Forecaster Brown

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Hurricane DARBY Forecast Discussion Number 19

2016-07-16 10:37:34| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SAT JUL 16 2016 000 WTPZ45 KNHC 160837 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 AM PDT SAT JUL 16 2016 Darby appears to be maintaining its strength. Satellite images indicate that the eye of the hurricane has become a bit more distinct and circular than it was several hours ago. Although the cloud tops have warmed a bit in the eyewall, the convective pattern is quite symmetric. A blend of the latest Dvorak classifications from TAFB and SAB, and automated values from CIMSS at the University of Wisconsin support holding the initial intensity at 90 kt. Although the wind shear is expected to remain light during the next several days, the oceanic conditions will soon become unfavorable for strengthening. Sea surface temperatures beneath the hurricane are expected to fall below 26 deg C in about 12 hours, and Darby is headed for even cooler waters after that. The cool waters combined with a progressively drier air mass should induce a gradual weakening trend beginning later today and continuing during the next several days. The NHC intensity forecast is largely an update of the previous one and is not too different from the intensity model consensus. Darby has been wobbling around during the past 12-18 hours, but smoothing through these positions yields an initial motion estimate of 295/9 kt. A gradual turn toward the west is expected during the next several days as a mid-level ridge builds to the north of the tropical cyclone. The model guidance is in fair agreement in the future track of Darby, and the NHC forecast lies close to the various consensus aids. An ASCAT pass from a few hours ago was helpful in estimating the size of the wind field of Darby. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 17.6N 123.1W 90 KT 105 MPH 12H 16/1800Z 18.0N 124.4W 85 KT 100 MPH 24H 17/0600Z 18.4N 126.0W 75 KT 85 MPH 36H 17/1800Z 18.8N 127.8W 70 KT 80 MPH 48H 18/0600Z 19.1N 129.8W 65 KT 75 MPH 72H 19/0600Z 19.8N 134.2W 50 KT 60 MPH 96H 20/0600Z 20.1N 138.9W 45 KT 50 MPH 120H 21/0600Z 19.5N 144.0W 40 KT 45 MPH $$ Forecaster Cangialosi

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Tropical Storm ESTELLE Forecast Discussion Number 3

2016-07-16 04:44:04| National Hurricane Center (East Pacific)

Issued at 900 PM MDT FRI JUL 15 2016 000 WTPZ41 KNHC 160243 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 900 PM MDT FRI JUL 15 2016 The convective structure of the tropical cyclone improved this evening with a curved band reaching halfway around its center. Correspondingly, the subjective TAFB and SAB Dvorak classifications each bumped up to a CI number of 2.5, or 35 kt. This is also consistent with the earlier scatterometer pass which showed a maximum of 30 kt at 17Z, when the convective structure was not as organized. Thus the system is now a tropical storm, both the fifth one of the eastern North Pacific season as well as the fifth one in a very busy two-week period. Estelle is moving toward the west-northwest at about 10 kt, south of an east-west oriented subtropical ridge. The cyclone should be steered toward the west or west-northwest at a slightly slower forward speed for the next few days. All of the reliable global and regional model track guidance are in close agreement and the NHC official track is nearly the same as that from the previous advisory. The intensity forecast, however, is a bit more uncertain. In the short term, the environment looks generally conducive with moderate northeasterly vertical shear, very warm water, and quite moist conditions. While the shear drops to very low values in about two days, Estelle should start moving over cooler water induced by the upwelling and mixing from the Blas-Celia-Darby trio of storms ahead of it. Thus it is anticipated that the cyclone should steadily intensify and then it may reach its peak strength at about day three. At the longer lead times, gradual weakening may commence if the track stays over the cooler water. This forecast is based upon the consensus of the Decay-SHIPS, LGEM, and HWRF models and is slightly higher than the previous advisory through day three and about the same at days four and five. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 15.2N 108.3W 35 KT 40 MPH 12H 16/1200Z 15.7N 109.6W 45 KT 50 MPH 24H 17/0000Z 16.1N 111.0W 55 KT 65 MPH 36H 17/1200Z 16.3N 112.6W 65 KT 75 MPH 48H 18/0000Z 16.7N 114.2W 75 KT 85 MPH 72H 19/0000Z 17.5N 117.1W 80 KT 90 MPH 96H 20/0000Z 18.1N 120.6W 75 KT 85 MPH 120H 21/0000Z 19.0N 125.0W 65 KT 75 MPH $$ Forecaster Landsea

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Hurricane DARBY Forecast Discussion Number 18

2016-07-16 04:44:04| National Hurricane Center (East Pacific)

Issued at 800 PM PDT FRI JUL 15 2016 000 WTPZ45 KNHC 160243 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 PM PDT FRI JUL 15 2016 Darby's eye became a little less well-defined and central convection weakened somewhat a few hours ago, and Dvorak data T-number from both TAFB and SAB were lowered to 4.5. Recently, however, cloud tops have been cooling around the eye and based on the Dvorak Current Intensity rules the maximum winds are kept at 90 kt for this advisory. The hurricane has well-defined upper-level outflow over all but the southeastern portion of the circulation. The tropical cyclone is in a weak-shear environment and is likely to remain so for the next several days. Whereas this would seem to favor the system to maintain strength or even intensify further, the future thermodynamic environment is not favorable. Darby is approaching a cold tongue in the ocean and should pass over SSTs near 24 deg C within a couple of days. Satellite imagery also shows an extensive stratocumulus field ahead of the hurricane, which is indicative of stabler air. These factors should cause Darby to be on a weakening trend very soon. The official intensity forecast is in close agreement with the model consensus, IVCN, and with the previous NHC forecast. Darby has moved a little more to the right of the previous track over the past several hours, but using a 12-hour average yields a motion estimate of 295/8. The mid-level flow on the south side of a subtropical ridge should cause the tropical cyclone to turn westward over the next several days. A slight northward adjustment was made to the official forecast, mainly due to the more northward short-term motion of Darby. The new official forecast lies on the southern side of the guidance envelope and is close to the latest GFS and ECMWF solutions, which are themselves in close agreement. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 17.3N 122.1W 90 KT 105 MPH 12H 16/1200Z 17.7N 123.4W 85 KT 100 MPH 24H 17/0000Z 18.1N 125.1W 80 KT 90 MPH 36H 17/1200Z 18.4N 126.7W 75 KT 85 MPH 48H 18/0000Z 18.7N 128.8W 70 KT 80 MPH 72H 19/0000Z 19.3N 133.3W 55 KT 65 MPH 96H 20/0000Z 20.0N 138.0W 45 KT 50 MPH 120H 21/0000Z 20.0N 142.5W 40 KT 45 MPH $$ Forecaster Pasch

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