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Tropical Storm Hilary Forecast Discussion Number 33

2017-07-29 16:34:54| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Jul 29 2017 000 WTPZ44 KNHC 291434 TCDEP4 Tropical Storm Hilary Discussion Number 33 NWS National Hurricane Center Miami FL EP092017 800 AM PDT Sat Jul 29 2017 Although Hilary has crossed the 25 deg SST isotherm, the inner-core of the tropical storm has remained mostly intact. Recent SSMI and AMSR microwave imagery indicate that deep convection is still present near the center of circulation, and in a band extending to the east and south. IR imagery from GOES-W even briefly showed a warm spot embedded within the shallow to medium convection that surrounds the center. Given that the cloud pattern hasn't changed significantly and an earlier ASCAT-A pass at 0540 UTC showed maximum winds of 49 kt, the initial intensity has been held at 55 kt. Despite Hilary's resilience so far, the SSTs beneath the cyclone will continue to decrease for the next several days, so weakening is inevitable. The intensity forecast has not been changed from the previous advisory, and shows Hilary becoming a remnant low within 48 hours. After days of high uncertainty, the track guidance is finally coming into better agreement. For the next 12 to 24 hours, Hilary should be steered generally toward the west-northwest or northwest by a mid-level ridge located to the north. After that time, a turn toward the west-northwest or west is expected due to a combination of interaction with Irwin and amplification of the ridge. Beyond day 3, the UKMET and ECMWF show the two cyclones dissipating in close proximity to one another, while the GFS still shows the systems merging. The NHC forecast favors the ECMWF and UKMET solutions for now, but both systems are expected to be very weak regardless of how close they actually get. The new track is just a little faster than the previous forecast and is close to the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 21.4N 121.5W 55 KT 65 MPH 12H 30/0000Z 22.4N 123.2W 50 KT 60 MPH 24H 30/1200Z 23.6N 125.6W 40 KT 45 MPH 36H 31/0000Z 24.6N 128.0W 30 KT 35 MPH 48H 31/1200Z 25.2N 130.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/1200Z 25.4N 132.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/1200Z 25.5N 134.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Irwin Forecast Discussion Number 29

2017-07-29 16:34:28| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Jul 29 2017 000 WTPZ45 KNHC 291434 TCDEP5 Tropical Storm Irwin Discussion Number 29 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Sat Jul 29 2017 Irwin's cloud pattern has not changed much since yesterday. It consists of a low-level center just to the north of a cyclonically curved convective band in the southern semicircle. An average of the Dvorak intensity estimates supports a 50-kt tropical cyclone. The circulation is still over warm waters and Irwin could maintain the same intensity for another 12 hours or so. After that time, the cyclone will begin to move over cooler waters resulting in gradual weakening. Models still disagree if Hilary and Irwin will merge as forecast by the GFS, or if both systems will dissipate nearby over cool waters as suggested by the ECMWF. The NHC forecast opts for the ECMWF proposal, but regardless of the solution, both system are anticipated to be weak remnant lows or may have even dissipated by then. Today, I found Irwin basically in the same spot I left it yesterday. It was anticipated that the cyclone was going to be meandering for a while within very weak steering currents, but it appears that this is about to change soon. Irwin will be influenced by the southerly flow in the wake of Hilary, and the cyclone should begin to move northward and northwestward with an increase in forward speed during the next 12 hours and beyond. The track forecast is similar to the previous one, and is basically on top of the multi-model consensus TVCX and TVCN which have been the models with the highest skill in forecasting Irwin so far. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 15.1N 124.9W 50 KT 60 MPH 12H 30/0000Z 16.2N 125.0W 50 KT 60 MPH 24H 30/1200Z 17.8N 125.2W 45 KT 50 MPH 36H 31/0000Z 20.1N 126.3W 40 KT 45 MPH 48H 31/1200Z 22.3N 127.8W 30 KT 35 MPH 72H 01/1200Z 26.0N 131.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/1200Z 27.5N 134.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/1200Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Irwin Forecast Discussion Number 28

2017-07-29 10:58:57| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Jul 29 2017 000 WTPZ45 KNHC 290858 TCDEP5 Tropical Storm Irwin Discussion Number 28 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Sat Jul 29 2017 Convection associated with Irwin has changed little over the past several hours, with weak convection in ragged bands occurring primarily in the southeastern semicircle. Satellite intensity estimates have also changed little since the last advisory, so the initial intensity remains 50 kt. Some strengthening is possible today while the storm remains over warm sea surface temperatures. After that, Irwin should weaken over waters that cool to near 23C near the 96 h forecast position. As mentioned in the discussion for Tropical Storm Hilary, the model guidance is diverse as to the eventual fate of Irwin as it interacts with Hilary, with the possibilities ranging from the early merger shown by the Canadian model to the ECMWF scenario of the two systems dissipating separately but in close proximity. The forecast leans more to the ECMWF solution and shows Irwin dissipating after 96 h to the north of Hilary or its remnants. Irwin is currently nearly stationary. A northward motion is expected to begin later today. Then, as the cyclone moves around the eastern and northern side of Hilary, a turn toward the north-northwest is expected in about 36 h, followed by a northwestward motion near the end of the cyclone's life. The new forecast track is similar to the previous track through 48 h, and it is shifted westward after that in agreement with the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 14.9N 124.9W 50 KT 60 MPH 12H 29/1800Z 15.7N 124.9W 55 KT 65 MPH 24H 30/0600Z 17.1N 125.1W 50 KT 60 MPH 36H 30/1800Z 19.2N 125.7W 45 KT 50 MPH 48H 31/0600Z 21.7N 127.0W 35 KT 40 MPH 72H 01/0600Z 25.5N 130.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/0600Z 27.5N 133.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Hilary Forecast Discussion Number 32

2017-07-29 10:45:57| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Jul 29 2017 000 WTPZ44 KNHC 290845 TCDEP4 Tropical Storm Hilary Discussion Number 32 NWS National Hurricane Center Miami FL EP092017 200 AM PDT Sat Jul 29 2017 The deep convection associated with Hilary has lost some organization since the last advisory, with little or no convection currently occurring over the western semicircle. Satellite intensity estimates range from 45-65 kt, and recent ASCAT data showed winds of at best 50 kt. Based on these, the initial intensity is nudged down to a possibly generous 55 kt. The system will be moving over progressively cooler water and into a more stable environment, which should cause a steady weakening. By 48 hours, Hilary is forecast to become a remnant low over 23C waters, and the cyclone is forecast to dissipate completely after 96 hr. The initial motion is now 305/9. As mentioned in the previous advisory, a mid-level ridge extending from southern California west-southwestward across the eastern Pacific should steer Hilary on this general path for the next couple of days. The forecast then gets more complicated due to potential interaction with TS Irwin. The guidance is in less good agreement than earlier, with the possibilities ranging from the Canadian model merging the two systems in 72 h to the ECMWF showing them dissipating in close proximity to one another near 120 h. The track guidance suggests a west-northwestward to westward turn for Hilary as Irwin or its remnants move around the eastern and northern sides, and the official forecast follows this scenario. The new forecast track is similar to the previous track for the first 36-48 h and then is nudged to the south thereafter. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 20.7N 120.8W 55 KT 65 MPH 12H 29/1800Z 21.7N 122.3W 50 KT 60 MPH 24H 30/0600Z 22.9N 124.3W 40 KT 45 MPH 36H 30/1800Z 24.1N 126.6W 30 KT 35 MPH 48H 31/0600Z 24.9N 128.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/0600Z 25.5N 131.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/0600Z 25.5N 133.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm HILARY Forecast Discussion Number 31

2017-07-29 04:34:26| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Fri Jul 28 2017 000 WTPZ44 KNHC 290234 TCDEP4 Tropical Storm Hilary Discussion Number 31 NWS National Hurricane Center Miami FL EP092017 800 PM PDT Fri Jul 28 2017 During the past few hours, a faint eye has emerged with Hilary on visible imagery, with even hints of a warm spot in the infrared channel. Overall, the satellite presentation has improved, and the subjective satellite intensity estimates have risen to between 55 and 65 kt. A blend of these values gives 60 kt for the initial intensity. This increase in winds should be short-lived since Hilary will be moving over progressively cooler water and into a more stable environment. By 48 hours, Hilary is forecast to become a remnant low over 22.5C waters. The latest NHC wind speed prediction is a blend of the previous interpolated forecast and the intensity consensus. Hilary continues moving northwestward, a little faster now at 10 kt. A mid-level ridge extending from southern California west-southwestward across the eastern Pacific should steer Hilary on this general path for the next couple of days. The forecast then gets more complicated due to any interaction with TS Irwin. Surprisingly, the model guidance has fallen into good agreement since the last cycle, displaying a slowdown for Hilary and a small turn to the west-northwest due to Irwin. The latest models are fairly close to the previous NHC forecast, so no significant changes are made. The other model trend of note is that none of the main global models shows Hilary absorbing Irwin, likely due to how weak Hilary will be in a few days. Instead Hilary just dissipates over the cold waters, and even a couple models have Irwin now absorbing Hilary since it will have a much shorter time over the poor environment. The NHC forecast will now show dissipation of the remnant low of Hilary by day 5, in accordance with all of the global models. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 20.3N 120.1W 60 KT 70 MPH 12H 29/1200Z 21.1N 121.4W 55 KT 65 MPH 24H 30/0000Z 22.3N 123.3W 50 KT 60 MPH 36H 30/1200Z 23.6N 125.4W 40 KT 45 MPH 48H 31/0000Z 24.7N 127.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 01/0000Z 25.8N 131.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/0000Z 26.5N 132.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/0000Z...DISSIPATED $$ Forecaster Blake

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