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Tropical Depression Greg Forecast Discussion Number 36

2017-07-26 10:50:43| Tropical Depression LIDIA

Issued at 200 AM PDT Wed Jul 26 2017

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Hurricane Irwin Forecast Discussion Number 16

2017-07-26 10:47:05| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Jul 26 2017 000 WTPZ45 KNHC 260846 TCDEP5 Hurricane Irwin Discussion Number 16 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Wed Jul 26 2017 An earlier 0500 UTC METOP-A AMSU image and fortuitous ASCAT A/B overpasses indicate that Irwin's circulation center is located near the southern edge of the cloud canopy. Apparently, the moderate southeasterly outflow produced by Hurricane Hilary is affecting Irwin's core structure. Cloud tops have warmed during the past several hours and a compromise of the Dvorak subjective T-numbers from SAB and TAFB support an initial intensity of 70 kt for this advisory. The global models as well as the statistical-dynamical intensity guidance show continued slow weakening during the next 36 hours while the hurricane remains within the impinging upper-level outflow of Hilary. Afterward, further gradual weakening is forecast as the cyclone traverses cooler oceanic temperatures and enters a less than favorable thermodynamic environment. The official forecast is similar to the previous package and is based on the IVCN consensus. The much anticipated turn toward the west-southwest has finally commenced, and the cyclone motion is estimated to be 255/6 kt. Some binary interaction with Hilary during the next 48 hours or so should cause Irwin to stall, and then accelerate cyclonically around the southeast through northeast periphery of Hilary on days 4 and 5. Global and ensemble models, however, show a much slower forward motion beyond 72 hours than what was indicated in the previous advisory, and adjustments to the 96 and 120 hour forecast periods have been made accordingly. The NHC forecast reflects this significant change in the guidance and is based a blend of the TVCX and HFIP Corrected Consensus (HCCA) models. The ASCAT 0502 UTC scatterometer data and the RVCN multi-model consensus were used for the initial and forecast wind radii. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 15.7N 121.5W 70 KT 80 MPH 12H 26/1800Z 15.5N 122.5W 65 KT 75 MPH 24H 27/0600Z 15.1N 123.7W 60 KT 70 MPH 36H 27/1800Z 14.8N 124.4W 55 KT 65 MPH 48H 28/0600Z 14.7N 124.7W 55 KT 65 MPH 72H 29/0600Z 14.9N 124.5W 55 KT 65 MPH 96H 30/0600Z 18.0N 124.5W 50 KT 60 MPH 120H 31/0600Z 20.5N 126.0W 45 KT 50 MPH $$ Forecaster Roberts

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Tropical Depression Greg Forecast Discussion Number 35

2017-07-26 04:57:15| Tropical Depression LIDIA

Issued at 800 PM PDT Tue Jul 25 2017

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Hurricane Irwin Forecast Discussion Number 15

2017-07-26 04:57:15| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 260256 TCDEP5 Hurricane Irwin Discussion Number 15 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Tue Jul 25 2017 Irwin has strengthened a little more during the past several hours. The eye of the hurricane has been occasionally evident in satellite images and cloud tops in the eyewall are quite cold, close to -80 C. The convective structure is asymmetric, however, with the majority of the deepest convection located to the west of the center. The latest Dvorak classifications have increased slightly, and support nudging the initial intensity upward to 80 kt. Irwin is moving westward at 7 kt as it is still being steered by a mid-level ridge to its northeast. A turn to the west-southwest is expected tonight and Wednesday as Hurricane Hilary approaches from the east. The forward motion of Irwin will likely come to a halt on Thursday and Friday as Hilary passes by to the north. After that time, a general northward motion is expected as Irwin gets caught in the flow on the east side of Hilary's circulation. The models are in better agreement compared to previous cycles, but there is still a fair amount of spread in where and when Irwin makes the northward turn. The NHC track forecast is largely an update of the previous one, and lies closest to the multi-model consensus TVCE. The hurricane could be nearing its peak intensity, and weakening should commence soon due to moderate wind shear and the potential for cold water upwelling due to the expected slow motion of Irwin. By the end of the forecast period, Irwin will be moving over much cooler SSTs and into a drier air mass, which should continue the weakening trend. The models are in good agreement, and the NHC intensity forecast lies near the middle of the guidance envelope. Irwin is a very compact hurricane. ASCAT data from around 1800 UTC indicated that the tropical storm force winds extend no more than 60 n mi from the center. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.1N 120.9W 80 KT 90 MPH 12H 26/1200Z 15.7N 121.9W 75 KT 85 MPH 24H 27/0000Z 15.2N 123.0W 70 KT 80 MPH 36H 27/1200Z 14.9N 123.8W 60 KT 70 MPH 48H 28/0000Z 14.7N 124.0W 55 KT 65 MPH 72H 29/0000Z 15.5N 123.5W 55 KT 65 MPH 96H 30/0000Z 18.2N 123.5W 55 KT 65 MPH 120H 31/0000Z 22.0N 126.0W 45 KT 50 MPH $$ Forecaster Cangialosi

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Hurricane Hilary Forecast Discussion Number 19

2017-07-26 04:50:03| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Tue Jul 25 2017 000 WTPZ44 KNHC 260249 TCDEP4 Hurricane Hilary Discussion Number 19 NWS National Hurricane Center Miami FL EP092017 900 PM MDT Tue Jul 25 2017 Hilary's convective cloud pattern has continued to fluctuate between an occasional symmetric appearance containing a cloud-covered eye to the current asymmetric pattern with little or no outer banding features evident and the eye completely obscured in conventional infrared imagery. However, recent SSMI, SSMIS, and AMSU microwave images still indicate that Hilary has a well-defined, 10-nmi-diameter eye and a thick eyewall beneath the cirrus canopy. Satellite intensity estimates range from T4.5/77 kt and T5.0/90 kt from TAFB and SAB, respectively, to T5.5/102 kt from the NHC Dvorak objective technique. Given the large range of estimates, the initial intensity will remain at 90 kt for now, which could be a little conservative. The initial motion remains a steady 285/10 kt. Hilary is forecast to continue on a general west-northwestward track for the next 72 hours or so. Thereafter, a slight bend toward the west with a decrease in forward speed is expected due to binary/Fujiwhara interaction with Hurricane Irwin. The forward speed difference between Hilary and Irwin is about 3-4 kt, with Hilary steadily getting closer to Irwin. That trend should continue on days 4 and 5 with the distance between the two cyclones decreasing to about 300 nmi, resulting in the two systems orbiting cyclonically about each other. Since Hilary is forecast to be the larger and more dominant circulation, Irwin's effect on Hilary's track is expected to be minimal. The latest NHC model guidance remains tightly clustered around the previous advisory track, so the new track forecast is just an extension of the previous advisory. Although SHIPS and UW-CIMMS shear analyses indicate north to northwesterly vertical wind shear of about 15 kt, there is no evidence of this shear based on water vapor imagery showing nearly symmetrical cirrus outflow and the eye being embedded in the center or south side of the CDO. The main inhibiting factor that has kept Hilary from strengthening appears to have been intermittent dry air intrusions into the inner-core region causing a brief erosion of the eyewall convection. Microwave data suggests that dry air remains nearby, so little if any intensification is forecast for the next 24 hours as a result. By 36 h and beyond, Hilary will be moving over sub-26C SSTs and upper-ocean heat content values near zero, and reaching 24C water on days 4 and 5. The decreasing thermodynamics should result in gradual weakening from 36-72 hours, with faster weakening thereafter. The new NHC intensity forecast closely follows the previous advisory and the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.0N 109.8W 90 KT 105 MPH 12H 26/1200Z 16.4N 111.5W 95 KT 110 MPH 24H 27/0000Z 16.9N 113.6W 90 KT 105 MPH 36H 27/1200Z 17.4N 115.7W 85 KT 100 MPH 48H 28/0000Z 18.0N 117.5W 80 KT 90 MPH 72H 29/0000Z 19.2N 121.1W 75 KT 85 MPH 96H 30/0000Z 20.0N 124.8W 60 KT 70 MPH 120H 31/0000Z 21.0N 128.3W 45 KT 50 MPH $$ Forecaster Stewart

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