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Tropical Storm BLAS Forecast Discussion Number 6

2016-07-04 10:54:14| National Hurricane Center (East Pacific)

Issued at 300 AM MDT MON JUL 04 2016 000 WTPZ43 KNHC 040854 TCDEP3 TROPICAL STORM BLAS DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP032016 300 AM MDT MON JUL 04 2016 During the past few hours, the satellite appearance of Blas has changed from consisting of primarily a long curved band to a large central dense overcast (CDO) feature. Recent AMSU data showed that a nearly closed mid-level eye feature with a diameter of about 35 nmi has also developed within the southwestern portion of the CDO. A 0420 UTC ASCAT pass revealed surface winds near 50 kt in the northeastern quadrant and a radius of maximum winds of about 30 nmi. UW-CIMSS ADT estimates were near 55 kt. These data support an intensity of 55 kt at 0600 UTC. However, since that time the satellite signature has improved, so the advisory intensity has been increased to 60 kt. The initial motion estimate remains a steady 285/10 kt. There is no significant change to the previous forecast reasoning and the latest NHC model guidance suite remains tightly packed. Therefore, the new forecast track is essentially just an update of the previous advisory track due to the subtropical ridge to the north of Blas remaining strong throughout the entire forecast period. The new NHC forecast closely follows the consensus model TVCE and basically lies down the middle of the guidance envelope. The atmospheric and oceanic environment is expected to be quite favorable for Blas to strengthen during the next 48-60 hours. Since the global models are forecasting Blas' outflow pattern to gradually expand and become more symmetrical, along with the development of both poleward and equator outflow channels, a period of rapid intensification is expected for at least the next 24 hours. Blas is expected to achieve its peak intensity around 48 hours or so when the vertical wind shear is forecast to be low at around 5 kt. After that, gradual weakening should begin by 72 hours when Blas will be moving over sub-26C SSTs, creating cold upwelling/mixing beneath the cyclone. The NHC intensity forecast is well above the consensus model IVCN, and closely follows the LGEM statistical-dynamical intensity model. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 12.7N 113.2W 60 KT 70 MPH 12H 04/1800Z 13.2N 114.8W 70 KT 80 MPH 24H 05/0600Z 13.8N 117.4W 85 KT 100 MPH 36H 05/1800Z 14.2N 119.8W 95 KT 110 MPH 48H 06/0600Z 14.8N 122.1W 105 KT 120 MPH 72H 07/0600Z 16.1N 126.5W 100 KT 115 MPH 96H 08/0600Z 17.5N 130.3W 80 KT 90 MPH 120H 09/0600Z 19.4N 133.6W 55 KT 65 MPH $$ Forecaster Stewart

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Tropical Storm BLAS Forecast Discussion Number 5

2016-07-04 04:36:14| National Hurricane Center (East Pacific)

Issued at 900 PM MDT SUN JUL 03 2016 000 WTPZ43 KNHC 040236 TCDEP3 TROPICAL STORM BLAS DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP032016 900 PM MDT SUN JUL 03 2016 The satellite presentation of Blas has not changed much since the previous advisory, with the cyclone featuring large convective bands and a developing CDO feature. A GCOM/AMSR-2 image from 2042 UTC showed a mid-level eye feature displaced about 30 n mi southwest of the low-level center, consistent with about 10 kt of northeasterly shear. Satellite classifications remain T3.5/55 kt from TAFB and SAB, and that is the initial intensity. The intensity forecast reasoning remains unchanged, as Blas should continue to strengthen at a steady rate for the next 48 hours over warm SSTs and in a low to moderate shear environment. After 48 hours the SSTs cool steadily along the forecast track, especially at days 4 and 5, and quick weakening is forecast by then. The NHC intensity forecast is close to or a bit above the SHIPS model at the high end of the guidance through 48 hours, and trends toward the weaker LGEM late in the period. Its worth noting that the HWRF and GFDL models are much weaker with Blas compared to the statistical models for this cycle. The initial motion estimate is 285/10. The dominant steering mechanism through the forecast period is a mid-level ridge centered over northern Mexico and extending westward across the eastern Pacific. This feature should steer Blas on a general westward to west-northwestward track through the forecast period. The track model guidance is in very good agreement with small spread through day 4, but the spread increases a bit at day 5. By then the GFS shows more of a poleward turn as the ridge is eroded by a closed mid/upper-level low northeast of the Hawaiian Islands, while the ECMWF and UKMET show less influence from the upper low. The new NHC forecast is close to a blend of the GFS and ECMWF solutions and is in the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 12.4N 112.2W 55 KT 65 MPH 12H 04/1200Z 12.9N 113.9W 65 KT 75 MPH 24H 05/0000Z 13.5N 116.4W 80 KT 90 MPH 36H 05/1200Z 14.0N 118.8W 90 KT 105 MPH 48H 06/0000Z 14.5N 121.2W 100 KT 115 MPH 72H 07/0000Z 15.9N 125.7W 105 KT 120 MPH 96H 08/0000Z 17.3N 129.5W 85 KT 100 MPH 120H 09/0000Z 19.1N 132.9W 60 KT 70 MPH $$ Forecaster Brennan

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Tropical Storm BLAS Forecast Discussion Number 4

2016-07-03 22:37:40| National Hurricane Center (East Pacific)

Issued at 300 PM MDT SUN JUL 03 2016 000 WTPZ43 KNHC 032037 TCDEP3 TROPICAL STORM BLAS DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP032016 300 PM MDT SUN JUL 03 2016 Blas' cloud pattern has not changed appreciably in organization since the previous advisory. Visible and microwave satellite imagery suggests that the cyclone's low-level center is located at the northern tip of a long band whose convective tops have been slowly warming. This structure suggests that Blas' rate of intensification is not as fast as was suspected earlier, possibly due to some northeasterly shear and likely the cyclone's large size. The initial intensity is set to 55 kt based on the latest Dvorak intensity estimates of T3.5 from TAFB and SAB. The initial motion estimate is a steady 285/11. There has been no change to the track forecast philosophy since the previous advisory. Blas is forecast to move west-northwestward throughout the forecast period along the southern periphery of a deep-layer subtropical ridge extending westward from northern Mexico. The GFS and ECMWF solutions have come into much better agreement beyond day 3, and the overall spread in the guidance is low through day 5. The new NHC forecast track is shifted to the north some, and lies very near the multi-model consensus. There does not appear to be anything conspicuous on the large scale that would prevent Blas from intensifying into a major hurricane during the next few days, and a large one at that. The NHC intensity forecast through day 3 is near or just below the statistical guidance, which is unanimously calling for Blas to become an intense hurricane. By 96 hours, even though the shear is forecast to remain low, the cyclone should be moving over steadily cooler waters and entering a drier and more stable environment. This should promote a weakening trend that will likely become more rapid by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 12.2N 111.4W 55 KT 65 MPH 12H 04/0600Z 12.8N 113.0W 65 KT 75 MPH 24H 04/1800Z 13.4N 115.4W 75 KT 85 MPH 36H 05/0600Z 13.9N 117.7W 90 KT 105 MPH 48H 05/1800Z 14.3N 120.0W 100 KT 115 MPH 72H 06/1800Z 15.5N 124.3W 110 KT 125 MPH 96H 07/1800Z 16.8N 128.6W 90 KT 105 MPH 120H 08/1800Z 18.4N 132.3W 70 KT 80 MPH $$ Forecaster Kimberlain

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Tropical Storm BLAS Forecast Discussion Number 3

2016-07-03 16:39:08| National Hurricane Center (East Pacific)

Issued at 900 AM MDT SUN JUL 03 2016 000 WTPZ43 KNHC 031439 TCDEP3 TROPICAL STORM BLAS DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP032016 900 AM MDT SUN JUL 03 2016 Satellite imagery indicates a marked increase in organization of the Blas' cloud pattern overnight, suggesting that the cyclone is quickly intensifying. The center is located underneath a ball of deep convection, the latter which appears to be a formative central dense overcast. The large-envelope cyclone also has a lengthening band that consists of very cold-topped convection in the shape of a figure six. Satellite classifications are T3.0/45 kt and T3.5/55 kt from SAB and TAFB at 1200 UTC, respectively. The initial intensity is raised to 50 kt, based on a blend of the two intensity estimates. The initial motion estimate is 285/11. Blas is forecast to move along the southern periphery of a deep-layer subtropical ridge centered over northern Mexico throughout the forecast period, which should keep the cyclone on a general west-northwesterly course. The model guidance is in very good agreement through 72 hours, but diverges after that time. The GFS and its ensemble mean lie near the previous forecast and is on the northern side of the guidance envelope, while the ECMWF and its ensemble mean are much farther south. The differences between the two models appear related to subtle variations in the strength and position of the subtropical ridge forecast after day 3. The NHC track forecast is adjusted a bit south of the previous one, on the southern side of the guidance envelope through 72 hours and near the multi-model consensus after that time. There does not appear to be anything obvious on the large-scale to impede intensification over the next few days, except that the cyclone will be very gradually departing the warmest waters over the basin. The light-easterly-shear, moist environment and warm waters should allow Blas to strengthen into a major hurricane as indicated in about 48 hours. The official NHC forecast through that time is heavily weighted toward the statistical guidance which is performing well, considering the current developmental trend. By 96 hours, even though the shear is forecast to remain low, the cyclone should be moving over steadily cooler waters and entering a drier and more stable environment. This should foster a weakening trend, though the weakening will likely occur only gradually. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 11.6N 110.3W 50 KT 60 MPH 12H 04/0000Z 12.1N 112.0W 60 KT 70 MPH 24H 04/1200Z 12.6N 114.1W 75 KT 85 MPH 36H 05/0000Z 13.1N 116.4W 90 KT 105 MPH 48H 05/1200Z 13.6N 118.7W 100 KT 115 MPH 72H 06/1200Z 14.6N 123.3W 105 KT 120 MPH 96H 07/1200Z 16.0N 127.7W 95 KT 110 MPH 120H 08/1200Z 17.3N 131.3W 85 KT 100 MPH $$ Forecaster Kimberlain

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Tropical Storm AGATHA Forecast Discussion Number 7

2016-07-03 16:34:39| Tropical Depression LIDIA

Issued at 800 AM PDT SUN JUL 03 2016

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