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Tropical Storm DARBY Forecast Discussion Number 33

2016-07-19 22:33:31| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE JUL 19 2016 000 WTPZ45 KNHC 192033 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 33 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 PM PDT TUE JUL 19 2016 Although Darby continues to exhibit a well-defined circulation, deep convection, in the form of ragged bands, continues to gradually diminish in coverage. The initial intensity is subsequently lowered to 55 kt and reflects the Dvorak intensity estimates from both TAFB and SAB. The cyclone is forecast to move over marginal SSTs and into a drier, more stable air mass with increasing modest southwesterly shear during the next several days. The official forecast indicates slight weakening during the next day or so, with very little change in strength through 96 hours as Darby traverses a slightly warmer ocean. Thereafter, Darby is expected to again weaken as it gains latitude and moves into a region of strong southwesterly shear. The official forecast is weighed heavily on the IVCN consensus and lies above the LGEM and Decay SHIPS. It should be noted that longer-range, i.e. day 4 and 5, intensity predictions have little skill. A series of microwave images reveal an apparent northward tilt with height of the cyclone. Consequently, the conventional satellite position estimates have been consistently a little north of the microwave fixes. Using a blend of these fixes, the initial motion is estimated at 280/11 kt. The synoptic reasoning for the track forecast has not changed, as Darby will be steered generally westward during the next 4 days. Through the remaining portion of the forecast, the cyclone is expected to decrease its forward speed and gradually begin to recurve northwestward into a growing weakness caused by an amplifying mid- to upper-level trough north of the Hawaiian Islands. The ECMWF global model has shifted farther south than the previous runs. This shift has also nudged the multi-model consensus south as well, and the official forecast follows suit and is close the GFS and ECMWF ensemble mean guidance. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 19.9N 136.6W 55 KT 65 MPH 12H 20/0600Z 20.0N 138.3W 50 KT 60 MPH 24H 20/1800Z 20.0N 140.6W 45 KT 50 MPH 36H 21/0600Z 19.7N 142.8W 45 KT 50 MPH 48H 21/1800Z 19.4N 145.1W 45 KT 50 MPH 72H 22/1800Z 19.2N 149.3W 45 KT 50 MPH 96H 23/1800Z 19.9N 152.0W 45 KT 50 MPH 120H 24/1800Z 21.6N 153.7W 40 KT 45 MPH $$ Forecaster Roberts

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Tropical Storm ESTELLE Forecast Discussion Number 17

2016-07-19 16:44:57| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE JUL 19 2016 000 WTPZ41 KNHC 191444 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 800 AM PDT TUE JUL 19 2016 Estelle has a well-defined low-level structure with an eye-feature noted in an early morning GPM microwave overpass. However, the convection surrounding the low-level center has not been particularity deep or persistent. Subjective Dvorak T-numbers from TAFB and SAB are 4.0, but objective estimates are lower and until the convection is able to maintain itself around the center, I have elected to maintain the previous intensity of 55 kt. Estelle has a little more than 24 hours remaining over warm water and in a low vertical wind shear environment. Most of the intensity guidance calls for little change in strength, but the NHC forecast will once again show Estelle reaching hurricane strength given the good low-level structure and seemingly favorable conditions. After 24 hours, Estelle will be moving over progressively cooler SSTs and into a less favorable thermodynamic conditions. This should lead to steady weakening and degeneration into a remnant low in 3 to 4 days. The tropical storm is moving west-northwest at 10 kt. Estelle is expected to move on a west to west-northwestward track to the south of a mid-level ridge that extends westward from northern Mexico. A mid- to upper-level forecast to drop south-southwestward between 140W and 150W is expected to erode the western portion of the ridge after day 3. As a result, Estelle is predicted to turn northwestward later in the forecast period. The model guidance continued to be in good agreement, and the new NHC track forecast is essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 18.8N 118.8W 55 KT 65 MPH 12H 20/0000Z 19.2N 120.5W 65 KT 75 MPH 24H 20/1200Z 19.6N 122.7W 60 KT 70 MPH 36H 21/0000Z 20.0N 125.2W 55 KT 65 MPH 48H 21/1200Z 20.7N 127.7W 45 KT 50 MPH 72H 22/1200Z 22.9N 132.8W 30 KT 35 MPH 96H 23/1200Z 26.0N 137.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 24/1200Z 29.5N 140.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm DARBY Forecast Discussion Number 32

2016-07-19 16:43:27| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE JUL 19 2016 000 WTPZ45 KNHC 191443 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 32 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 AM PDT TUE JUL 19 2016 Conventional satellite imagery shows that the inner core cloud tops have warmed since last night and deep convective banding has become fragmented. Although Darby has exhibited an intermittent ragged eye feature, a blend of the subjective Final-T and CI-numbers, and the objective ADT estimate, yield an intensity of 60 kt. Additionally, the ambiguity solution of an earlier ASCAT overpass revealed only a couple of 50-55 kt winds over the northern quadrant. Accordingly, Darby's initial intensity has been lowered to 60 kt for this advisory. The cyclone is currently traversing sub-25C water, but should be moving back over slightly warmer water east of the Hawaiian Islands near the 36 hour period. Darby, however, will also be moving into a more stable thermodynamic environment and modest southwesterly shear around the same time. Therefore, these contributing factors are expected to cause Darby to gradually weaken through the period. The official intensity forecast is based primarily on the model consensus, IVCN, which includes the HWRF hurricane model, and is above both the SHIPS and LGEM statistical-dynamical intensity models. The track forecast philosophy remains similar to the previous forecast. The cyclone should continue on a generally westward heading to the south of a mid-tropospheric ridge anchored along 30N for the next few days. At the 96 hour period, Darby is forecast to slow its forward speed as it encounters a growing weakness in the ridge while a mid- to upper-level low digs north of the Hawaiian Islands. This synoptic feature should turn Darby gradually northwestward, east of the Big Island. The NHC forecast is located between the TVCE multi-model consensus and both the GFS and ECMWF ensemble mean guidance which are both situated north of the Hawaiian Islands. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 19.8N 135.4W 60 KT 70 MPH 12H 20/0000Z 20.1N 137.1W 55 KT 65 MPH 24H 20/1200Z 20.1N 139.3W 50 KT 60 MPH 36H 21/0000Z 20.1N 141.5W 50 KT 60 MPH 48H 21/1200Z 19.7N 143.8W 45 KT 50 MPH 72H 22/1200Z 19.4N 148.1W 45 KT 50 MPH 96H 23/1200Z 19.9N 151.2W 40 KT 45 MPH 120H 24/1200Z 21.6N 153.4W 35 KT 40 MPH $$ Forecaster Roberts

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Hurricane DARBY Forecast Discussion Number 31

2016-07-19 10:34:23| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE JUL 19 2016 000 WTPZ45 KNHC 190834 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 AM PDT TUE JUL 19 2016 Although deep convection has been decreasing since the previous advisory, Darby still has a well-defined and tight circulation. The initial intensity is held at 65 kt, in agreement with the Dvorak CI-numbers from TAFB and SAB, but the automated values from CIMSS at the University of Wisconsin suggest that this estimate could be a little generous. Microwave data indicate that the low-level center of Darby is located to the south of the eye feature seen in infrared satellite images, which is likely the result of southerly shear. Using the microwave fixes, the initial motion estimate is 285/11 kt. A continued west-northwestward motion is expected today, followed by a motion slightly south of due west on Wednesday while Darby is steered by a narrow mid-level ridge to its north. By the end of the forecast period, a turn to the northwest is predicted when Darby approaches a trough to the north of the Hawaiian Islands. The new NHC track forecast is slightly faster than the previous one to come in line with latest runs of the GFS and ECMWF models. Darby is expected to remain over cool water for the next few days, before it tracks over SSTs around 26 deg C to the east of the Hawaiian Islands. However, the system will also be moving into an environment of increasing southwesterly shear by the time it reaches the warmer water. Therefore, gradual weakening is predicted through the period. This forecast is the same as the previous one and is in best agreement with the LGEM guidance. An ASCAT-B pass from around 0600 UTC was helpful in estimating the size of Darby's wind field. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 19.4N 134.4W 65 KT 75 MPH 12H 19/1800Z 19.8N 136.1W 60 KT 70 MPH 24H 20/0600Z 20.0N 138.3W 55 KT 65 MPH 36H 20/1800Z 20.0N 140.5W 50 KT 60 MPH 48H 21/0600Z 19.8N 142.8W 45 KT 50 MPH 72H 22/0600Z 19.3N 147.3W 35 KT 40 MPH 96H 23/0600Z 19.4N 150.9W 35 KT 40 MPH 120H 24/0600Z 20.5N 153.0W 30 KT 35 MPH $$ Forecaster Cangialosi

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Tropical Storm ESTELLE Forecast Discussion Number 15

2016-07-19 04:40:54| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON JUL 18 2016 000 WTPZ41 KNHC 190240 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 800 PM PDT MON JUL 18 2016 The satellite presentation of Estelle has degraded a bit in the past few hours with some warming cloud-top temperatures noted near the center. Convective towers have been seemingly just rotating around the center without any appreciable increase in inner-core structure. Satellite classifications have dropped a bit, so the initial wind speed will be lowered to 55 kt for this advisory. It is a little puzzling why Estelle has not intensified but it is likely related to the cyclone's large size and radius of maximum wind, along with any lingering dry mid-level air. With Estelle remaining over warm water and experiencing light shear for the next day or so, it makes sense to think the earlier negative conditions would eventually be overcome. There is a split tonight in the guidance, however, with the statistical-dynamical aids (SHIPS/LGEM) basically showing no intensification, while the regional dynamical models (HWRF/GFDL) are forecasting Estelle to become a hurricane. Given what has occurred so far, it is prudent to drop the intensity forecast from the previous one, but not yet give up on Estelle becoming a hurricane. A more consistent weakening should begin in a couple of days over cool waters, with remnant low status likely by day 4. Microwave and satellite data indicate that Estelle continues to move west-northwestward. A large ridge over the eastern Pacific has been providing a steady steering current for the cyclone. Estelle should continue moving westward to west-northwestward for the next several days, then turn northwestward late in the forecast period due to a weakness in the ridge. The track guidance continues to be tightly clustered, and the NHC forecast remains very close to the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 18.3N 116.5W 55 KT 65 MPH 12H 19/1200Z 18.7N 117.9W 60 KT 70 MPH 24H 20/0000Z 19.1N 120.1W 65 KT 75 MPH 36H 20/1200Z 19.4N 122.4W 60 KT 70 MPH 48H 21/0000Z 19.9N 124.9W 50 KT 60 MPH 72H 22/0000Z 21.6N 130.3W 40 KT 45 MPH 96H 23/0000Z 24.0N 135.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 24/0000Z 27.5N 139.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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