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Hurricane DARBY Forecast Discussion Number 24

2016-07-17 16:36:52| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SUN JUL 17 2016 000 WTPZ45 KNHC 171436 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 AM PDT SUN JUL 17 2016 Darby's satellite presentation has changed very little since the last advisory. The hurricane still has a well-defined 10 n mi wide eye and a symmetric central dense overcast with cloud tops as cold as -68C. The initial intensity is held at 85 kt based on a blend of the latest Dvorak Current Intensity numbers, which are 5.0/90 kt from TAFB and SAB and 4.7/82 kt from the UW-CIMSS ADT. A narrow subtropical ridge lies to the north of the hurricane along 30N, which is steering Darby westward, or 280/8 kt. A westward or west-northwestward motion is expected during the next four days due to the position and strength of the ridge, and the track guidance is in excellent agreement during this period. By day 5, a weaker Darby is forecast to turn west-southwestward due to strong low-level ridging north of the Hawaiian Islands. There is a little more spread among the track models at the end of the forecast period, but the GFS, ECMWF, and UKMET are all south of the TVCE multi-model consensus. The updated forecast therefore remains south of TVCE and is a little faster than the previous forecast on day 5. Darby is now over SSTs between 24 and 25C and is expected to move over even colder waters in 12-24 hours. Therefore, fairly quick weakening is forecast in the short term, and Darby is likely to lose hurricane strength on Monday. SSTs are actually expected to begin increasing again after 24 hours, which could slow the rate of weakening through the end of the forecast period. However, increasing vertical shear and a drier mid-level air mass by days 4 and 5 will likely prevent significant re-intensification over the warmer waters to the southeast of Hawaii. The NHC intensity forecast is near the SHIPS model through day 3 and then a little higher than SHIPS on days 4 and 5, closer to the ICON intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 18.3N 127.4W 85 KT 100 MPH 12H 18/0000Z 18.4N 128.8W 75 KT 85 MPH 24H 18/1200Z 18.8N 130.9W 65 KT 75 MPH 36H 19/0000Z 19.3N 133.1W 55 KT 65 MPH 48H 19/1200Z 19.7N 135.4W 50 KT 60 MPH 72H 20/1200Z 20.1N 140.2W 40 KT 45 MPH 96H 21/1200Z 19.5N 145.0W 35 KT 40 MPH 120H 22/1200Z 18.5N 150.0W 35 KT 40 MPH $$ Forecaster Berg

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Tropical Storm ESTELLE Forecast Discussion Number 8

2016-07-17 10:47:48| National Hurricane Center (East Pacific)

Issued at 300 AM MDT SUN JUL 17 2016 000 WTPZ41 KNHC 170847 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 300 AM MDT SUN JUL 17 2016 A large increase in both the areal coverage and depth of the central convective cloud mass has occurred since the previous advisory due to the development of a irregularly shaped CDO. Cloud tops near the alleged center have been -80C and colder during the past couple of hours. Recent SSMI/S and AMSU microwave passes indicate that the low-level circulation center has become better defined, and has also moved closer to the strongest convection and farther into the CDO. As a result, satellite intensity estimates from TAFB and SAB have increased to a consensus T3.5/55 kt. However, UW-CIMSS ADT and NHC objective Dvorak estimates are only T2.8/41 kt and T3.0/45 kt, respectively. Given that the aforementioned microwave images still indicated some southward tilt to the mid-level center due to modest northerly vertical shear, the initial intensity has only been increased to 50 kt for this advisory. The initial motion estimate is westward or 280/08 kt. A motion between west and west-northwest is expected for the next 96 hours as Estelle moves along the southern periphery of a strong deep-layer to its north. After that time, a strong mid-latitude upper-level trough/low currently located near 25N/119W is forecast to dig southwestward and erode the ridge, allowing Estelle to turn northwestward into the developing weakness in the subtropical high. The new NHC model guidance remains tightly packed, and the official forecast track is just an update of the previous advisory track, and follows a blend of the GFS, ECMWF, and Florida State Superensemble (FSSE) models. Moderate northerly to northwesterly shear is forecast to affect Estelle for the next 36 hours, so only modest intensification is expected. After that, however, the vertical shear is forecast to decrease to around 5 kt through the end of the period, resulting in more substantial strengthening through 72 h while the cyclone remains over favorable SSTs. By 96 h, gradual weakening is forecast to ensue as Estelle begins to move over sub-25C ocean temperatures. The NHC intensity forecast is similar to the previous advisory, and remains above the model consensus IVCN and the SHIPS/LGEM models, but close to the FSSE intensity forecast. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 16.2N 111.1W 50 KT 60 MPH 12H 17/1800Z 16.6N 112.2W 60 KT 70 MPH 24H 18/0600Z 17.1N 113.7W 65 KT 75 MPH 36H 18/1800Z 17.6N 115.3W 70 KT 80 MPH 48H 19/0600Z 17.8N 117.1W 75 KT 85 MPH 72H 20/0600Z 18.3N 121.1W 85 KT 100 MPH 96H 21/0600Z 18.9N 125.8W 70 KT 80 MPH 120H 22/0600Z 20.7N 131.1W 50 KT 60 MPH $$ Forecaster Stewart

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Hurricane DARBY Forecast Discussion Number 22

2016-07-17 04:36:40| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SAT JUL 16 2016 000 WTPZ45 KNHC 170236 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 PM PDT SAT JUL 16 2016 Darby has finally responded to the cooler SSTs, with a weakening in the central convection and the eye becoming less distinct. The current intensity is reduced to 90 kt which is a blend of Data-T and Current Intensity numbers. The cyclone is expected to traverse ocean waters of near 25 deg C, along the northern edge of the strong gradient of SST, for the next few days. Even though the shear is forecast to remain low for the next 2-3 days, the combination of cooler waters and a more stable air mass should result in continued weakening. Near the end of the forecast period, the SSTs under Darby will begin to warm a bit. By that time, however, increasing west-southwesterly shear should prevent restrengthening. Center fixes are in good agreement, which is not surprising given that an eye has been apparent, and the initial motion continues at 285/9 kt. A narrow mid-level subtropical ridge to the north of Darby is expected to remain in place for the next several days. This steering pattern should cause the tropical cyclone to move on a mainly westward heading for the next 4 days or so. By the end of the forecast period, the weakening system should be steered more by the low-level tradewind flow, and turn to a slightly south of westward heading. The official track forecast is very close to the previous one, and is a blend of the latest GFS and ECMWF solutions. A drifting buoy, ID 46906, near the southern eyewall of Darby, measured a pressure of 980.1 mb around 0200 UTC. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 18.2N 125.8W 90 KT 105 MPH 12H 17/1200Z 18.4N 127.2W 85 KT 100 MPH 24H 18/0000Z 18.7N 129.1W 75 KT 85 MPH 36H 18/1200Z 18.9N 131.2W 65 KT 75 MPH 48H 19/0000Z 19.1N 133.2W 55 KT 65 MPH 72H 20/0000Z 19.8N 138.0W 45 KT 50 MPH 96H 21/0000Z 19.6N 142.5W 40 KT 45 MPH 120H 22/0000Z 18.5N 147.5W 35 KT 40 MPH $$ Forecaster Pasch

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Tropical Storm ESTELLE Forecast Discussion Number 6

2016-07-16 22:33:23| National Hurricane Center (East Pacific)

Issued at 300 PM MDT SAT JUL 16 2016 000 WTPZ41 KNHC 162033 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 300 PM MDT SAT JUL 16 2016 Estelle's satellite presentation has changed very little since this morning, with a large convective band still wrapping around the western and southwestern portion of the circulation. Satellite data show that there is some northerly shear affecting Estelle, causing a north-south tilt between the low- and mid-level centers and a lack of convection over the northern part of the storm. Dvorak intensity estimates are unchanged since this morning and the initial intensity remains 45 kt, which is in agreement with a recent CIMSS AMSU intensity estimate. The northerly shear is forecast to relax during the next day or so, which should allow for strengthening while the tropical cyclone remains over warm water during the next few days. Estelle is expected to become a hurricane in about 24 hours, and reach peak intensity in 2 to 3 days. The NHC intensity forecast is again a little above the SHIPS/LGEM guidance, but in close agreement with the Florida State Super Ensemble (FSSE). The low-level center has been difficult to pinpoint today as several low cloud swirls have been rotating around a mean center. Based on the recent fixes of the mean center, the initial motion estimate is 290/7 kt. The tropical cyclone should continue on a west-northwestward heading during the next few days to the south of a subtropical ridge that extends westward from northern Mexico. The GFS continues to show less ridging than the ECMWF and has a track that is along the northern edge of the guidance envelope. Meanwhile, the ECMWF depicts a stronger ridge and a track more westward. The NHC track lies between these solutions and is again close to the FSSE. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 15.8N 109.7W 45 KT 50 MPH 12H 17/0600Z 16.2N 110.8W 55 KT 65 MPH 24H 17/1800Z 16.7N 112.2W 65 KT 75 MPH 36H 18/0600Z 17.2N 113.7W 70 KT 80 MPH 48H 18/1800Z 17.7N 115.3W 75 KT 85 MPH 72H 19/1800Z 18.4N 118.9W 85 KT 100 MPH 96H 20/1800Z 18.9N 123.2W 80 KT 90 MPH 120H 21/1800Z 20.3N 128.3W 60 KT 70 MPH $$ Forecaster Brown

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Hurricane DARBY Forecast Discussion Number 21

2016-07-16 22:33:05| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SAT JUL 16 2016 000 WTPZ45 KNHC 162033 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 PM PDT SAT JUL 16 2016 Darby appears to have been strengthening during the day despite moving over increasingly cooler waters. The deep convection is becoming more symmetric, the eye has been warming intermittently, and the hurricane appears to be losing some of its outer banding. In fact, Darby has developed a marginal annular structure. Dvorak estimates have generally risen since this morning, and the initial intensity is raised to 100 kt. This makes Darby the second major hurricane of the eastern North Pacific season. Sea surface temperatures beneath Darby are currently around 25.5C and will continue to decrease over the next few days. But, given that vertical shear is expected to remain low through at least day 3, and the hurricane's marginal annular structure, Darby is likely to remain relatively steady in intensity or only gradually weaken in the short-term. Faster weakening is still expected later in the forecast period due to the added effect of increasing shear. Almost every reliable intensity model shows Darby weakening fast during the next day or two. However, the HWRF model is a notable outlier and keeps Darby as a hurricane at least through day 3. The updated NHC intensity forecast is a little higher than the previous forecast during the first 36 hours and is near the top end of the main pack of intensity models. The initial motion remains 285/9 kt. The subtropical ridge to the north of Darby is weakening, but it should stay strong enough to steer the hurricane west-northwestward or westward through the entire forecast period. The new run of the ECMWF has sped up compared to the other track models, but otherwise there is very little spread in the guidance envelope. The updated NHC track forecast is closest to an average of the GFS and ECMWF and is very close to the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 18.0N 124.9W 100 KT 115 MPH 12H 17/0600Z 18.3N 126.3W 90 KT 105 MPH 24H 17/1800Z 18.5N 128.1W 80 KT 90 MPH 36H 18/0600Z 18.8N 130.1W 70 KT 80 MPH 48H 18/1800Z 19.0N 132.2W 60 KT 70 MPH 72H 19/1800Z 19.7N 136.6W 50 KT 60 MPH 96H 20/1800Z 19.7N 141.1W 40 KT 45 MPH 120H 21/1800Z 18.7N 146.0W 35 KT 40 MPH $$ Forecaster Berg

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