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Hurricane Irwin Forecast Discussion Number 13

2017-07-25 16:35:59| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 251435 TCDEP5 Hurricane Irwin Discussion Number 13 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Tue Jul 25 2017 Recent microwave imagery confirms that Irwin has a well-defined mid-level eye, which has also been apparent in shortwave infrared satellite imagery. On the whole, satellite intensity estimates have risen a little, so Irwin's initial intensity is now set at 70 kt. Various shear analyses indicate that about 15 kt of southerly shear has developed over Irwin, which isn't surprising since microwave data has hinted that the low-level center may be located just a bit south of the mid-level eye. This shear is expected to continue for another 24 hours or so, which will likely prevent Irwin from any additional significant strengthening. After 24 hours, Irwin's proximity to Hurricane Hilary is likely to induce some weakening, as well as the potential for upwelling of colder water due to Irwin's slow motion through 72 hours. More definitive weakening is likely by day 5 as Irwin reaches higher latitudes and much colder waters. The intensity models are fairly stable at the moment the latest runs did not suggest that any changes were needed to the previous forecast. It should be noted that while most of the global models maintain Irwin as a separate and distinct cyclone from Hilary through day 5, the ECMWF model indicates that Irwin could be absorbed by that time. Irwin appears to be moving slowly westward, or 270/5 kt. The cyclone's future track will largely be dictated its the binary interaction with Hilary. First, as Hilary approaches from the east, Irwin is expected to dip west-southwestward and southwestward during the first 48 hours. It will likely stall by day 3, but then get pulled northward and northwestward around the eastern side of Hilary's circulation. Although there is still considerable spread in the track models after 72 hours, the regional HWRF and HMON models are now on board with the binary interaction. Therefore, the NHC track forecast is much closer to the TVCN multi-model consensus than it has been during the past few days. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 15.6N 119.4W 70 KT 80 MPH 12H 26/0000Z 15.2N 120.2W 70 KT 80 MPH 24H 26/1200Z 14.7N 121.4W 65 KT 75 MPH 36H 27/0000Z 14.2N 122.2W 60 KT 70 MPH 48H 27/1200Z 13.9N 122.8W 55 KT 65 MPH 72H 28/1200Z 14.4N 122.7W 55 KT 65 MPH 96H 29/1200Z 18.0N 122.0W 55 KT 65 MPH 120H 30/1200Z 21.5N 125.0W 50 KT 60 MPH $$ Forecaster Berg

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Hurricane HILARY Forecast Discussion Number 16

2017-07-25 10:58:33| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Tue Jul 25 2017 000 WTPZ44 KNHC 250858 TCDEP4 Hurricane Hilary Discussion Number 16 NWS National Hurricane Center Miami FL EP092017 300 AM MDT Tue Jul 25 2017 Hilary's compact, symmetric, inner core continues to become better defined on satellite imagery. Microwave imagery suggests that the eye is quite small, less than 10 n mi in diameter, with little evidence of vertical tilt of the vortex. The current intensity estimate is now 90 kt in agreement with a Dvorak estimate from the NESDIS SAB. Hilary should be in a moist air mass and over a warm ocean for the next couple of days. Dynamical guidance predicts some increase in northerly shear over the cyclone in 1- to 2-days, but probably not enough of an increase to impede at least some additional strengthening. The official intensity forecast calls for Hilary to become a major hurricane in 12 hours or so and reach a peak in a day or so. This is in good agreement with the latest Florida State University Superensemble (FSSE) prediction. Later in the forecast period, gradually cooling sea surface temperatures should induce slow weakening. The initial motion estimate remains west-northwestward, or 290/9 kt. A mid-tropospheric ridge extending westward from the southwestern United States would cause Hilary to continue on its west-northwestward track for the next several days. In a few days, however, Hilary is likely to pass close to Hurricane Irwin. The current thinking is that the circulation of Hilary will dominate so that little influence on Hilary's track, due to binary interaction with Irwin, will occur. On the other hand, the latter tropical cyclone is expected to begin rotating around Hilary's circulation later in the forecast period (please refer to the Forecast Discussion on Irwin for additional information). The official track forecast is quite close to the simple consensus TVCN, and to the corrected consensus predictions, HCCA and FSSE. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 15.3N 106.7W 90 KT 105 MPH 12H 25/1800Z 15.8N 108.2W 100 KT 115 MPH 24H 26/0600Z 16.3N 110.4W 105 KT 120 MPH 36H 26/1800Z 16.8N 112.6W 105 KT 120 MPH 48H 27/0600Z 17.4N 114.8W 100 KT 115 MPH 72H 28/0600Z 18.6N 118.7W 85 KT 100 MPH 96H 29/0600Z 19.5N 122.5W 75 KT 85 MPH 120H 30/0600Z 20.0N 126.0W 65 KT 75 MPH $$ Forecaster Pasch

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Hurricane Irwin Forecast Discussion Number 12

2017-07-25 10:58:33| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 250858 TCDEP5 Hurricane Irwin Discussion Number 12 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Tue Jul 25 2017 Deep convection associated with Irwin now wraps almost all of the way around the center, and there have been occasional hints of a eye in microwave and conventional satellite imagery. Subjective satellite estimates from TAFB and SAB are just below hurricane strength, while several objective estimates, including the CIMSS satellite consensus, are above hurricane strength. With the attempts at eye formation, the initial intensity will lean toward the higher intensity estimates, and thus Irwin is upgraded to a hurricane. The initial motion is a little more northward than before at 300/4. A slow westward motion is forecast today as a weak mid-level ridge remains in place to the north of the storm. A west-southwestward motion is expected between 24-72 h as Hurricane Hilary approaches from the east. After that, Irwin is expected to undergo an binary interaction with Hilary, with the most likely result for Irwin being a generally northward motion around the eastern semicircle of Hilary. The details of this are still uncertain, with the ECMWF and Canadian models merging the two cyclones before 120 h, while the GFS and UKMET keep them separate until after 120 h. The new track forecast is similar to the previous forecast through 72 h. After that, it leans towards the GFS/UKMET in keeping the cyclone separate and accelerating Irwin around the eastern side of Hilary. Little change in strength is likely for the next 24 h. After that, increasing shear associated with the outflow of Hilary is likely to cause Irwin to weaken, although there is considerable spread in the guidance as to how much shear and how much weakening. By the end of the forecast period, cooler water along the forecast track and proximity to Hilary should cause additional weakening. The new forecast track is a slight adjustment of the previous track. An alternative intensity scenario is that Irwin dissipates as it is absorbed by Hilary before 120 h. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 15.5N 118.7W 65 KT 75 MPH 12H 25/1800Z 15.3N 119.4W 65 KT 75 MPH 24H 26/0600Z 15.0N 120.5W 65 KT 75 MPH 36H 26/1800Z 14.6N 121.4W 60 KT 70 MPH 48H 27/0600Z 14.3N 122.2W 55 KT 65 MPH 72H 28/0600Z 14.0N 123.0W 55 KT 65 MPH 96H 29/0600Z 16.0N 122.5W 55 KT 65 MPH 120H 30/0600Z 20.0N 123.0W 50 KT 60 MPH $$ Forecaster Beven

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Tropical Storm Greg Forecast Discussion Number 32

2017-07-25 10:54:58| Tropical Depression LIDIA

Issued at 200 AM PDT Tue Jul 25 2017

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Hurricane Hilary Forecast Discussion Number 15

2017-07-25 04:35:58| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Mon Jul 24 2017 000 WTPZ44 KNHC 250235 TCDEP4 Hurricane Hilary Discussion Number 15 NWS National Hurricane Center Miami FL EP092017 1000 PM CDT Mon Jul 24 2017 Recent microwave satellite images indicate that Hilary has developed a tight banding eye feature with a diameter of less than 10 nmi. Deep convection with cloud tops to -85C within an elongated CDO has continued to pulse since the previous advisory, likely due to some modest high-level shear induced by a large convective complex located a couple hundred nmi southeast of Hilary's center. However, that convective cloud mass has recently been showing signs of waning, so that negative influence will likely begin to abate fairly soon. Dvorak satellite intensity estimates were a consensus T4.5/77 kt from TAFB and SAB at 0000Z. Since that time, the CDO has become more distinct and NHC objective intensity estimates have been ranging between 82-88 kt during the past 2 hours. As a result, the advisory intensity has been increased to 85 kt. The initial motion estimate is 300/08 kt. Hilary is forecast to move generally west-northwestward along the southern periphery of a deep-layer subtropical ridge for the next 5 days. With the exception of the more northerly GFS model -- which had a similar poleward bias with Fernanda -- the rest of the NHC model guidance is tightly clustered around the previous forecast track. As a result, only minor speed adjustments were made to the previous forecast track. Although some binary interaction with TS Irwin is still possible, Hilary is expected to be the larger and more dominant circulation, resulting in Irwin being pulled poleward within Hilary's wake on days 3-5. The small eye and tight inner-core banding features noted in recent microwave imagery, along with large-scale low vertical wind shear conditions and favorable thermodynamics, argues for some rapid intensification to occur during the next 12-24 hours. Thereafter, some adjustment of the eye and inner-core wind field is possible, which has resulted in a leveling off of Hilary's intensity forecast in the 24-to 48-h period. By 72 hours and beyond, the combination of decreasing SSTs to less than 26C along with some modest westerly wind shear should produce steady weakening. The official intensity forecast is similar to the previous advisory, and follows a blend of the HCCA and ECMWF intensity predictions. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 15.0N 105.7W 85 KT 100 MPH 12H 25/1200Z 15.5N 107.0W 95 KT 110 MPH 24H 26/0000Z 16.1N 109.0W 105 KT 120 MPH 36H 26/1200Z 16.5N 111.1W 105 KT 120 MPH 48H 27/0000Z 17.1N 113.0W 100 KT 115 MPH 72H 28/0000Z 18.1N 116.7W 90 KT 105 MPH 96H 29/0000Z 19.1N 120.2W 80 KT 90 MPH 120H 30/0000Z 19.9N 123.4W 65 KT 75 MPH $$ Forecaster Stewart

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