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Tropical Storm Hilary Forecast Discussion Number 36

2017-07-30 10:51:05| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Jul 30 2017 000 WTPZ44 KNHC 300850 TCDEP4 Tropical Storm Hilary Discussion Number 36 NWS National Hurricane Center Miami FL EP092017 200 AM PDT Sun Jul 30 2017 Deep convection associated with Hilary has continued to decrease in coverage overnight, with only a small area of cold cloud tops remaining to the southeast of the center. An average of the Dvorak T- and CI-numbers from TAFB, SAB, and UW-CIMMS yields an initial intensity estimate of 40 kt. Hilary will be moving into a more stable airmass over SSTs below 22C very soon, which should result in steady weakening over the next 24 to 48 hours. Deep convection is also expected to dissipate later today, and Hilary is forecast to degenerate to a remnant low within 24 hours. Recent satellite fixes show that Hilary has turned west- northwestward or 300/12 kt. A west-northwestward motion between a low- to mid-level ridge to the north and Tropical Storm Irwin to the south should continue over the next couple of days. The latest global models suggest that cyclone is likely to dissipate before any merger with Irwin or its remnants takes place. The NHC track forecast is along the southern portion of the tightly clustered guidance and is very similar to the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 23.5N 124.7W 40 KT 45 MPH 12H 30/1800Z 24.4N 126.7W 35 KT 40 MPH 24H 31/0600Z 25.4N 129.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 31/1800Z 26.0N 131.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 01/0600Z 26.3N 132.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 02/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Hilary Forecast Discussion Number 35

2017-07-30 04:34:04| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Jul 29 2017 000 WTPZ44 KNHC 300233 TCDEP4 Tropical Storm Hilary Discussion Number 35 NWS National Hurricane Center Miami FL EP092017 800 PM PDT Sat Jul 29 2017 Satellite data indicate that Hilary is gradually losing organization. GOES-16 1-minute visible data show the center on the northwestern side of a warming central dense overcast. A late-arriving ASCAT-A pass from 1808Z suggested maximum winds of up to 55 kt. With the degradation in the satellite presentation since that time, the initial wind speed is set to 50 kt. While Hilary has been holding its own recently, the cold waters and dry stable air mass of the eastern Pacific always end up winning, and a steady weakening of Hilary should begin soon. The intensity forecast is close to a blend of the previous interpolated forecast and the HFIP-corrected intensity consensus. Transition to a remnant low is expected in about 24 hours due to Hilary moving over progressively colder waters. Hilary is moving a little faster and to the left, now 305/12. The storm should turn west-northwestward as it weakens and begins to interact with the circulation of Irwin. There is a reasonable consensus in the models that one or both of the tropical cyclones will dissipate before any merger can occur, and none of the major models keep Hilary intact through 72 hours. Thus the only change is to show Hilary dissipated at that time, with only cosmetic modifications made to the rest of the forecast. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 22.9N 123.7W 50 KT 60 MPH 12H 30/1200Z 23.9N 125.5W 40 KT 45 MPH 24H 31/0000Z 25.0N 128.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 31/1200Z 25.8N 130.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 01/0000Z 26.0N 132.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 02/0000Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm Irwin Forecast Discussion Number 31

2017-07-30 04:32:34| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Jul 29 2017 000 WTPZ45 KNHC 300232 TCDEP5 Tropical Storm Irwin Discussion Number 31 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Sat Jul 29 2017 Irwin had a partially cloud-free region near its center in visible satellite imagery a few hours ago, but that feature has since filled, and cloud-top temperatures have cooled in the central region. Satellite intensity estimates range widely from 35 kt to 55 kt, but an ASCAT pass from around 1800 UTC showed maximum winds just over 40 kt in the southeastern quadrant. Based on that data, the initial intensity is lowered to 45 kt. Although the shear over the cyclone is low and should remain low for several days, Irwin only has another 12 hours or so before it reaches waters colder than 26 deg C. Therefore, additional weakening is anticipated after 12 hours, and Irwin could degenerate into a remnant low as early as 48 hours while it is over sea surface temperatures of 22 deg C. Based on a consensus of the global models, the remnant low should dissipate by day 5. Irwin is accelerating toward the north as anticipated, and the initial motion is now 355/7 kt. The cyclone should turn north-northwestward soon and continue accelerating during the next 36 hours in the wake of Tropical Storm Hilary. After 48 hours, once the two remnant circulations get even closer together, Irwin is likely to turn northwestward and slow down considerably. There is a normal amount of spread among the track guidance, and the updated NHC track forecast was only shifted slightly northeast of the previous forecast on days 3 and 4 to lean closer to the ECMWF, HCCA, and the various multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 16.4N 124.6W 45 KT 50 MPH 12H 30/1200Z 17.7N 125.0W 45 KT 50 MPH 24H 31/0000Z 19.9N 126.0W 40 KT 45 MPH 36H 31/1200Z 22.3N 127.4W 35 KT 40 MPH 48H 01/0000Z 24.6N 128.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0000Z 27.4N 132.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 03/0000Z 28.5N 133.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 04/0000Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Hilary Forecast Discussion Number 34

2017-07-29 22:37:27| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Jul 29 2017 000 WTPZ44 KNHC 292037 TCDEP4 Tropical Storm Hilary Discussion Number 34 NWS National Hurricane Center Miami FL EP092017 200 PM PDT Sat Jul 29 2017 The inner-core of Hilary continues to feature deep convection, despite analyzed SSTs below 24 deg C. At times during the day today, an eye or eye-like feature has even been observed in IR and visible imagery. That said, an ASCAT-B pass at 1722 UTC revealed maximum winds of only 46 kt in the NW quadrant. Based on the ASCAT data, the initial intensity has been lowered to 50 kt, suggesting that Hilary has finally begun to weaken. The intensity forecast is unchanged and steady weakening is expected until the cyclone becomes a remnant low, now shown to occur in about 36 hours. All of the global models forecast that Hilary will dissipate within 4 days, in close proximity to Irwin. The initial motion is 310/11 kt, and Hilary has been slipping a little to the right of the forecast track today, perhaps in part due to the fact that it has maintained a fairly coherent deep circulation. A turn back toward the west-northwest is still expected within the next 12-24 hours as the tropical storm weakens and interacts with the circulation of Irwin. The various global models still differ in the details of that interaction, but generally agree that both systems will be weak and one or the other will probably dissipate before a merger can occur. Overall, the NHC track has been shifted slightly to the right to account for the initial motion, but is otherwise unchanged from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 22.3N 122.5W 50 KT 60 MPH 12H 30/0600Z 23.3N 124.2W 45 KT 50 MPH 24H 30/1800Z 24.4N 126.7W 35 KT 40 MPH 36H 31/0600Z 25.2N 129.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 31/1800Z 25.5N 130.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/1800Z 25.5N 132.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Irwin Forecast Discussion Number 30

2017-07-29 22:33:30| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Jul 29 2017 000 WTPZ45 KNHC 292033 TCDEP5 Tropical Storm Irwin Discussion Number 30 NWS National Hurricane Center Miami FL EP102017 200 PM PDT Sat Jul 29 2017 Irwin's cloud pattern continues to be defined by a low-level center located just to the north of a cyclonically curved convective band in the southern semicircle. Dvorak intensity estimates are beginning to indicate weakening, and a recent partial ASCAT pass shows maximum winds of 40 kt. However, given the banding-type eye structure observed on visible images, the initial intensity is kept at 50 kt. 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 are now showing that Irwin and Hilary will get very close to each other while dissipating. Irwin is forecast to become a remnant low by 72 hours and is expected to be dissipated by day 5. Irwin began to move toward the north or 360 degrees at 6 kt. Soon the cyclone will be steered by the flow in the wake of Hilary and turn more to the north-northwest and northwest with increasing forward speed. There is no significant change from the previous forecast which continues to be very close to the multi-model consensus primarily during the next 3 days. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 15.6N 124.5W 50 KT 60 MPH 12H 30/0600Z 16.7N 124.7W 50 KT 60 MPH 24H 30/1800Z 18.7N 125.3W 45 KT 50 MPH 36H 31/0600Z 21.0N 126.5W 40 KT 45 MPH 48H 31/1800Z 23.5N 128.0W 30 KT 35 MPH 72H 01/1800Z 26.5N 131.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/1800Z 27.5N 134.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/1800Z...DISSIPATED $$ Forecaster Avila

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