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Tropical Storm Emilia Forecast Discussion Number 7

2018-06-29 10:38:41| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Fri Jun 29 2018 000 WTPZ41 KNHC 290838 TCDEP1 Tropical Storm Emilia Discussion Number 7 NWS National Hurricane Center Miami FL EP062018 200 AM PDT Fri Jun 29 2018 Emilia has changed little in organization since the previous advisory, with the convection continuing to be displaced to the west and southwest of the low-level center by 15-20 kt of easterly vertical wind shear. The initial intensity remains 45 kt based on a blend of various satellite intensity estimates. The initial motion is a somewhat uncertain 300/10. A low- to mid-level subtropical ridge to the north of Emilia should steer the cyclone generally west-northwestward through the forecast period, and the track guidance is in good agreement with this scenario. The new forecast track is an update of the previous forecast. The dynamical model guidance suggests that the shear should gradually decrease during the next 24-48 h. However, the sea surface temperatures along the forecast track decrease during this time, and it is uncertain if Emilia will be able to take advantage of the more favorable upper-level winds. The new forecast follows the trend of the previous forecast in showing slight strengthening during this time. After 48 h, the cyclone is expected to move over cool enough waters to cause steady weakening, and Emilia is currently forecast to decay to a remnant low by 96 h. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 16.0N 115.3W 45 KT 50 MPH 12H 29/1800Z 16.5N 116.8W 50 KT 60 MPH 24H 30/0600Z 17.2N 118.7W 55 KT 65 MPH 36H 30/1800Z 17.8N 120.5W 55 KT 65 MPH 48H 01/0600Z 18.4N 122.2W 50 KT 60 MPH 72H 02/0600Z 20.0N 126.0W 40 KT 45 MPH 96H 03/0600Z 21.5N 129.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 04/0600Z 23.0N 133.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Storm Emilia Forecast Discussion Number 6

2018-06-29 04:32:09| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Thu Jun 28 2018 000 WTPZ41 KNHC 290232 TCDEP1 Tropical Storm Emilia Discussion Number 6 NWS National Hurricane Center Miami FL EP062018 900 PM MDT Thu Jun 28 2018 Several microwave images during the day revealed that Emilia continues to be a sheared cyclone with the center to the east of a convective mass. However, it appears that during the past hour or so, the center is a little closer to the edge of the thunderstorm activity, and Dvorak T-numbers are now indicative of a 45-kt tropical cyclone. Model guidance is not showing much decrease in the northeasterly shear for the next 24 to 36 h, and this scenario only allows for slight strengthening. In addition, by the time the shear is forecast to decrease, the circulation of Emilia will be affected by cooler waters. By then, a decay in intensity is anticipated. Emilia is moving toward the west-northwest or 290 degrees at about 10 kt, steered by the flow around a narrow subtropical ridge to the north of the cyclone. Most of the global models indicate that the ridge will persist for the next several days, and the forecast flow pattern should keep Emilia on the same general track until dissipation. The NHC forecast is very similar to the previous one and follows very closely the HFIP Corrected Consensus (HCCA), which is in the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 15.4N 114.5W 45 KT 50 MPH 12H 29/1200Z 16.0N 116.0W 50 KT 60 MPH 24H 30/0000Z 16.6N 117.8W 55 KT 65 MPH 36H 30/1200Z 17.3N 119.7W 55 KT 65 MPH 48H 01/0000Z 18.0N 121.5W 50 KT 60 MPH 72H 02/0000Z 19.7N 125.0W 40 KT 45 MPH 96H 03/0000Z 21.5N 129.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 04/0000Z 23.0N 133.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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Tropical Storm Emilia Forecast Discussion Number 5

2018-06-28 22:31:36| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Thu Jun 28 2018 000 WTPZ41 KNHC 282031 TCDEP1 Tropical Storm Emilia Discussion Number 5 NWS National Hurricane Center Miami FL EP062018 300 PM MDT Thu Jun 28 2018 Satellite images indicate that Emilia is better organized than this morning, with a large banding feature wrapping around the western semicircle. There is still a fair amount of northeasterly shear, however, since the eastern part of the circulation is partially exposed. A blend of the Dvorak estimates from TAFB and SAB gives an initial wind speed of 40 kt. Further strengthening is expected over the next day or so while Emilia experiences decreasing shear over warm waters. A gradual decline in intensity should begin over the weekend due to the storm encountering cooler SSTs and entraining drier more stable air. Model guidance is a bit higher with the peak intensity of Emilia on this cycle, and the official prediction follows suit, ending up near the corrected consensus models. The storm continues to move west-northwestward this afternoon. A gradual decrease in Emilia's forward speed should occur over the next few days due to a weakening mid-level ridge to the north. The global models are still indicating a break in the subtropical ridge persisting at long range, which would keep the west-northwestward motion going throughout the period. The only change to the track forecast is a northward adjustment at days 4 and 5 to better match the poleward-trending models, although the official forecast remains on the southern side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 14.9N 113.6W 40 KT 45 MPH 12H 29/0600Z 15.5N 115.2W 45 KT 50 MPH 24H 29/1800Z 16.2N 117.1W 55 KT 65 MPH 36H 30/0600Z 16.9N 118.9W 55 KT 65 MPH 48H 30/1800Z 17.5N 120.5W 50 KT 60 MPH 72H 01/1800Z 19.0N 123.8W 40 KT 45 MPH 96H 02/1800Z 21.0N 127.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 03/1800Z 22.5N 131.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Tropical Storm Emilia Forecast Discussion Number 4

2018-06-28 16:37:01| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Thu Jun 28 2018 000 WTPZ41 KNHC 281436 TCDEP1 Tropical Storm Emilia Discussion Number 4 NWS National Hurricane Center Miami FL EP062018 900 AM MDT Thu Jun 28 2018 Deep convection continues in the western semicircle of the cyclone, although a fair portion of the eastern side of the low-level circulation is exposed due to shear. Satellite classifications are essentially the same as 6 hours ago, so the initial wind speed will stay 35 kt. Global models are in good agreement that the wind shear will decrease over the next 24 hours, which should promote strengthening. In a couple of days, Emilia is predicted to move over cool SSTs and through a drier environment, causing its inevitable weakening to begin. The official forecast is essentially an update of the previous one, showing a gradual increase in strength until late Friday, then weakening on Sunday. Emilia should become a remnant low by 96 hours as it moves over SSTs of about 23C. Emilia has been a challenging storm to track because of limited microwave passes and an elongated low-level structure. Even with 1-min GOES-16 visible data, it is difficult to tell how embedded the center of Emilia is within the deep convection. The available data suggest the storm has slowed a little bit and turned to the right, so my motion estimate is 290/12 kt. A mid-level ridge over Mexico and the adjacent eastern Pacific should gradually weaken during the next few days, resulting in a reduction of Emilia's forward speed. The biggest change from the last forecast cycle is that there could be a more substantial break in the subtropical ridge in the medium-range period, allowing the storm to continue a more west-northwestward motion, rather than taking a climatological westward turn. This track is dependent on how strong the cyclone is at that time and, since Emilia is forecast to be rather weak at long range, the official forecast is on the southern side of the guidance envelope, albeit with a northward adjustment since the last advisory. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 14.4N 112.4W 35 KT 40 MPH 12H 29/0000Z 15.1N 114.1W 40 KT 45 MPH 24H 29/1200Z 15.9N 116.2W 45 KT 50 MPH 36H 30/0000Z 16.6N 118.0W 50 KT 60 MPH 48H 30/1200Z 17.2N 119.7W 50 KT 60 MPH 72H 01/1200Z 18.6N 123.0W 40 KT 45 MPH 96H 02/1200Z 20.5N 126.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 03/1200Z 21.5N 131.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Tropical Storm Emilia Forecast Discussion Number 3

2018-06-28 10:55:21| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Thu Jun 28 2018 000 WTPZ41 KNHC 280855 TCDEP1 Tropical Storm Emilia Discussion Number 3 NWS National Hurricane Center Miami FL EP062018 300 AM MDT Thu Jun 28 2018 Convection has steadily increased and become better organized since the previous advisory, especially in the inner-core region. Satellite intensity estimates at 0600 UTC were T2.0/30 kt from both TAFB and SAB, and T2.3/33 kt from UW-CIMSS ADT. Since that time, however, convection near the low-level center has increased, resulting in a steady increase in the raw ADT estimates to T2.5/35 kt. Based on the latter data, the initial intensity is increased to 35 kt at the advisory time, making Emilia the fifth tropical storm so far this season as well as the fifth tropical storm so far during the month of June. The motion estimate is an uncertain 285/13 kt due to uncertainty in the exact location of the low-level center. Passive microwave satellite data, plus extrapolation of the previous motion, were used to locate the center. However, recent GOES-16 nighttime cloud physics satellite data suggest that the center may be developing closer to the ball of strong convection in the southern portion of the north-to-southwest elongated circulation. Having said that, the latest model guidance remains in fair agreement on Emilia moving in a general west-northwestward direction during the next 96 hours, accompanied by a gradual decrease in forward speed. Afterwards, what should be a weakened and more shallow cyclone is expected to be turned westward by a strong subtropical ridge and brisk easterly tradewind flow. The GFS and UKMET models take Emilia more northwestward into the strong subtropical ridge after 72 hours, which seems unlikely. As a result, the new track forecast is similar to the previous advisory, which lies near the southern edge of the guidance envelope and close to a blend of the ECMWF and HWRF models. Emilia's outflow is good to the west but restricted to the east due to near 20 kt of easterly vertical wind shear. The shear is forecast to decrease to around 15 kt by 48 hours and to less than 10 kt by 72 h and beyond. This should allow for some modest strengthening during the next 48 h while the cyclone remains over SSTs greater than 26 deg C. After that time, however, SSTs drop off sharply to less than 25C, and the cooler water temperatures are expected to combine with much drier mid-level to induce a steady weakening trend despite the favorable shear environment. The new NHC intensity forecast is essentially just the same as the previous advisory, and is slightly higher the consensus intensity model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 13.8N 111.3W 35 KT 40 MPH 12H 28/1800Z 14.4N 113.1W 35 KT 40 MPH 24H 29/0600Z 15.2N 115.2W 40 KT 45 MPH 36H 29/1800Z 15.9N 117.0W 45 KT 50 MPH 48H 30/0600Z 16.5N 118.8W 50 KT 60 MPH 72H 01/0600Z 17.6N 121.8W 45 KT 50 MPH 96H 02/0600Z 19.1N 125.3W 35 KT 40 MPH 120H 03/0600Z 20.3N 129.8W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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