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Hurricane Hilary Forecast Discussion Number 23

2017-07-27 04:37:55| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Wed Jul 26 2017 000 WTPZ44 KNHC 270237 TCDEP4 Hurricane Hilary Discussion Number 23 NWS National Hurricane Center Miami FL EP092017 900 PM MDT Wed Jul 26 2017 Recent microwave images indicate that Hilary is vertically titled due to 15-20 kt of northwesterly shear. Although the low-level center of the hurricane is still located beneath very cold cloud tops, the overall cloud pattern appears more ragged than it was earlier today. The Dvorak classifications from TAFB and SAB have held steady at 5.0/90 kt, but based on the degraded appearance and structure, the initial wind speed is lowered a little to 85 kt. This intensity estimate is between the above mentioned subjective Dvorak estimates and the ADT values from CIMSS at the University of Wisconsin. The moderate shear currently affecting Hilary is expected to continue for about another day, which should cause some additional weakening. Even though the shear should lessen beyond 24 hours, Hilary will be moving over progressively cooler waters and it is forecast to cross the 26 degree C isotherm in about 2 days. These less favorable oceanic conditions and a progressively drier and more stable air mass should cause additional weakening, and Hilary is expected to become a post-tropical cyclone by the end of the forecast period. The NHC intensity forecast is a little lower than previous one, and it is close to the HFIP and IVCN consensus models. The hurricane is moving west-northwestward at 10 kt steered by a mid-level ridge to its northeast. The track forecast philosophy has not changed from the past few advisories. Although some interaction may take place with Irwin, currently located about 500 nmi to the west of Hilary, it is not expected to have much of an impact on the future path of Hilary. A general track to the west-northwest at a slightly slower pace is expected throughout the forecast period. The new NHC track forecast is similar to the previous one, and it is in best agreement with the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 17.1N 114.2W 85 KT 100 MPH 12H 27/1200Z 17.4N 115.6W 80 KT 90 MPH 24H 28/0000Z 17.9N 117.2W 75 KT 85 MPH 36H 28/1200Z 18.6N 118.8W 75 KT 85 MPH 48H 29/0000Z 19.3N 120.5W 70 KT 80 MPH 72H 30/0000Z 20.7N 124.3W 60 KT 70 MPH 96H 31/0000Z 21.8N 128.1W 45 KT 50 MPH 120H 01/0000Z 22.9N 131.2W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Cangialosi

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Tropical Depression Greg Forecast Discussion Number 37

2017-07-26 16:51:41| Tropical Depression LIDIA

Issued at 500 AM HST Wed Jul 26 2017

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Tropical Storm Irwin Forecast Discussion Number 17

2017-07-26 16:50:37| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Wed Jul 26 2017 000 WTPZ45 KNHC 261450 TCDEP5 Tropical Storm Irwin Discussion Number 17 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Wed Jul 26 2017 Satellite images and microwave data indicate that Irwin's cloud pattern has significantly deteriorated since yesterday. It now consists of a tight circulation center located just to the south of an area of deep, but not too well organized, convection. Consequently, the initial intensity has been decreased to 55 kt based on lower Dvorak T-numbers from all agencies. The environment does not support significant weakening, but is not favorable for much intensification either. The NHC forecast calls for a slight weakening today, and shows no change in intensity for the next 5 days. Although the intensity forecast is a little bit different from the previous one due to the lower current intensity, it does not change the general trend expressed in previous NHC forecasts. Irwin is moving toward the west-southwest or 255 degrees at 6 kt. Currently, the cyclone is embedded within weak steering currents, and Irwin will probably continue on the same slow west-southwest track during the next day or two. After that time, Hurricane Hilary is forecast to pass well north of Irwin, and the steering currents will change to southerlies, and most of the models agree that Irwin should begin to move with a northerly component in the wake of Hilary. This is reflected in the official NHC forecast which in fact is close to the multi-model consensus TVCN, and is not very different from the previous one. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 15.6N 122.1W 55 KT 65 MPH 12H 27/0000Z 15.3N 123.0W 45 KT 50 MPH 24H 27/1200Z 14.9N 124.1W 45 KT 50 MPH 36H 28/0000Z 14.5N 125.0W 45 KT 50 MPH 48H 28/1200Z 14.5N 125.5W 45 KT 50 MPH 72H 29/1200Z 15.0N 125.0W 45 KT 50 MPH 96H 30/1200Z 17.5N 125.0W 45 KT 50 MPH 120H 31/1200Z 20.5N 126.0W 45 KT 50 MPH $$ Forecaster Avila

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Hurricane Hilary Forecast Discussion Number 21

2017-07-26 16:36:09| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Wed Jul 26 2017 000 WTPZ44 KNHC 261435 TCDEP4 Hurricane Hilary Discussion Number 21 NWS National Hurricane Center Miami FL EP092017 900 AM MDT Wed Jul 26 2017 Satellite images indicate that Hilary remains a powerful hurricane. The central dense overcast has become more symmetric, although convection is still preferentially forming in the eastern eyewall. Any eye feature, however, is somewhat less distinct than a few hours ago, and the latest microwave passes are again showing an open eyewall on the west side. Intensity estimates range from 82 to 99 kt, so the initial wind speed will stay at 90 kt. There are still hints of northerly shear in cirrus cloud motions from the 1-min GOES-16 data, although the cyclone's cloud canopy looks less distorted than yesterday. This shear is forecast to persist for the next day or two while the hurricane moves over warm waters. After that time, while the shear could decrease, Hilary will be traversing marginally warm waters, with some increase in drier, more stable air in the environment. Most of the guidance is in good agreement on little change in the short-term, with a gradual decrease in wind speed through 3 days. Beyond then, much colder waters should cause a more rapid weakening, along with some interaction with Irwin. The new NHC forecast is basically an update of the previous one and lies close to IVCN, the variable intensity model consensus. It should be noted that the ECMWF is on its own by intensifying Hilary to a major hurricane in 2 to 3 days. The initial motion is 280/11. The track forecast is essentially unchanged for the next 48 h, while Hilary is expected to be steered by the mid-level subtropical ridge to the north. After that time, the ridge is forecast to become weaker to due to a mid- to upper-level trough dropping over the Baja California peninsula. Models are not in good agreement on how much the ridge weakens due to this trough, leading to a wide disparity of solutions at long range. There has been little change in the guidance suite since 6z, so the official forecast is close to the previous one. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 16.4N 112.3W 90 KT 105 MPH 12H 27/0000Z 16.7N 113.9W 90 KT 105 MPH 24H 27/1200Z 17.1N 115.7W 90 KT 105 MPH 36H 28/0000Z 17.5N 117.4W 85 KT 100 MPH 48H 28/1200Z 18.1N 118.9W 80 KT 90 MPH 72H 29/1200Z 19.7N 121.9W 75 KT 85 MPH 96H 30/1200Z 21.4N 125.4W 55 KT 65 MPH 120H 31/1200Z 23.0N 129.0W 35 KT 40 MPH $$ Forecaster Blake

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Hurricane Hilary Forecast Discussion Number 20

2017-07-26 10:56:39| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Wed Jul 26 2017 000 WTPZ44 KNHC 260856 TCDEP4 Hurricane Hilary Discussion Number 20 NWS National Hurricane Center Miami FL EP092017 300 AM MDT Wed Jul 26 2017 The structure of Hilary has changed little during the past several hours. Conventional satellite imagery shows a central dense overcast that is slightly elongated north-to-south, most likely due to the impact of some northerly shear. An eye is occasionally appearing in infrared imagery, and microwave data continues to indicate an eye present under the overcast. However, the eye has not yet become well-developed enough to justify an increase in the initial intensity, which remains 90 kt in agreement with a blend of the various satellite estimates. The initial motion is 285/11. The track forecast is essentially unchanged for the next 72 h, while Hilary is expected to be steered by the mid-level subtropical ridge to the north. After that time, the guidance has become increasingly divergent due to disagreements on how much a mid- to upper-level trough just west of California affects the ridge. The GFS uses the trough to break the ridge and allow Hilary to move almost northward by the end of the period, which is a major shift to the right since the previous advisory. The UKMET and Canadian models keep the strongest ridge and forecast a more westward motion. The ECMWF is between these extremes, but has shifted northward since the previous advisory. An additional complication is the possibility of interaction with Hurricane Irwin. The new GFS forecast calls for little interaction, while the UKMET and Canadian merge the two cyclones in 3-4 days and the ECMWF has interaction at days 4-5. The latter part of the new forecast track will be moved northward based on the northward shift of the GFS, ECMWF, and the various consensus models. However, it lies to the south of the consensus models and the center of the guidance envelope in deference to the UKMET and Canadian forecasts. This part of the forecast is low confidence and additional adjustments may be needed later. Some slight strengthening is possible today even though Hilary is in marginal shear conditions. After that, the cyclone should move over progressively cooler sea surface temperatures and gradually weaken. The new intensity forecast has changed little through 72 hours, and then shows a faster rate of decay based on a track over colder water than previously forecast. It should be noted that the uncertainty in the track forecast also affects the intensity forecast, as either a more northward motion or interaction with Irwin would probably weaken the cyclone faster than currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 16.3N 111.0W 90 KT 105 MPH 12H 26/1800Z 16.7N 112.7W 95 KT 110 MPH 24H 27/0600Z 17.1N 114.7W 90 KT 105 MPH 36H 27/1800Z 17.6N 116.5W 85 KT 100 MPH 48H 28/0600Z 18.1N 118.2W 80 KT 90 MPH 72H 29/0600Z 19.5N 121.5W 75 KT 85 MPH 96H 30/0600Z 21.0N 125.0W 55 KT 65 MPH 120H 31/0600Z 22.5N 128.5W 35 KT 40 MPH $$ Forecaster Beven

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