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Potential Tropical Cyclone Fourteen Forecast Discussion Number 1

2018-10-06 22:50:32| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sat Oct 06 2018 000 WTNT44 KNHC 062050 TCDAT4 Potential Tropical Cyclone Fourteen Discussion Number 1 NWS National Hurricane Center Miami FL AL142018 400 PM CDT Sat Oct 06 2018 Satellite imagery and surface observations indicate that the circulation of the low pressure area in the northwestern Caribbean Sea is getting better defined, and that the associated convection is becoming better organized. While the system is currently not well enough organized to call it a tropical depression, current indications in the global models and the intensity guidance are that the system will develop into a tropical cyclone within 24 h and could bring tropical storm conditions to portions of western Cuba and the northeastern Yucatan Peninsula. Based on the need for warnings and watches in these areas, advisories are being initiated on Potential Tropical Cyclone Fourteen. Although the intensity guidance is in excellent agreement that the system should strengthen through the forecast period, the global models indicate that shear caused by an upper-level trough over the Gulf of Mexico will persist through at least 48 h. In addition, the strongest winds are currently well removed from the center, which is likely to slow development. Based on this, the intensity forecast is in the lower part of the guidance envelope through 48 h, and then shows a faster rate of development from 48-96 h when the shear is forecast to diminish. The intensity forecast is closest to a blend of the IVCN and HCCA consensus models. For the first 24-48 h, the disturbance should move generally northward on the western side of a weak mid-level ridge over the Caribbean Sea. After that time, a large mid-latitude trough over the central United States and a mid- to upper-level ridge over the western Atlantic should steer the system generally northward at a faster forward speed, with the system expected to move near or over the northern Gulf coast in about 96 h. After landfall, the system is likely to recurve northeastward into the westerlies. The track guidance is in good overall agreement with this scenario. However, it should be noted that there is a nearly 300 n mi cross-track spread in the guidance at the 96-h point. The forecast track lies just to the west of the various consensus models. Key Messages for Potential Tropical Cyclone Fourteen: 1. This system is expected to produce heavy rainfall and flash flooding over portions of Central America, western Cuba, and the northeastern Yucatan Peninsula of Mexico during the next couple of days. The system is also forecast to become a tropical storm by Sunday night and tropical storm conditions are expected over portions of western Cuba where a Tropical Storm Warning is in effect. 2. The system could bring storm surge, rainfall, and wind impacts to portions of the northern Gulf Coast by mid-week, although it is too soon to specify the exact location and magnitude of these impacts. Residents in these areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 18.0N 86.6W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 07/0600Z 18.7N 86.7W 25 KT 30 MPH 24H 07/1800Z 19.9N 86.6W 30 KT 35 MPH...TROPICAL CYCLONE 36H 08/0600Z 21.0N 86.6W 35 KT 40 MPH 48H 08/1800Z 22.5N 86.7W 40 KT 45 MPH 72H 09/1800Z 26.0N 87.5W 55 KT 65 MPH 96H 10/1800Z 30.5N 86.5W 60 KT 70 MPH 120H 11/1800Z 35.5N 81.5W 30 KT 35 MPH...INLAND $$ Forecaster Beven

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Tropical Storm Leslie Forecast Discussion Number 42

2018-10-06 22:37:32| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Oct 06 2018 000 WTNT43 KNHC 062037 TCDAT3 Tropical Storm Leslie Discussion Number 42 NWS National Hurricane Center Miami FL AL132018 500 PM AST Sat Oct 06 2018 The central convection associated with Leslie is still well organized and concentrated. A recent SSMIS image shows that Leslie's inner core is better defined resembling an eyewall. However, Dvorak estimates still support an initial intensity intensity of 50 kt. Leslie should weaken slightly during the next 24 to 36 h as the cyclone crosses patches of cooler SSTs. After that time, the track takes the center back over warmer waters, but the shear could increase a little. Only minor adjustments are made to the previous intensity forecast, and the NHC forecast follows very close the model consensus which suggests slight strengthening by the end of the forecast period. Leslie continues to be embedded within the mid-latitude westerlies and is moving toward the east or 100 degrees at 10 kt. These westerlies are forecast to be modulated by the passage of short waves, and the flow pattern will initially keep Leslie on east to east-southeast track for most of the forecast period. By the end of the period a turn to the northeast is anticipated. Models are not in great agreement but they are consistently showing the eastward progression of the cyclone. The NHC forecast is very close to the models consensus, and is basically in the middle of the track envelope. Large swells generated by Leslie are expected to continue during the next few days across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 37.4N 54.5W 50 KT 60 MPH 12H 07/0600Z 37.1N 52.8W 45 KT 50 MPH 24H 07/1800Z 36.6N 50.4W 45 KT 50 MPH 36H 08/0600Z 35.8N 48.0W 45 KT 50 MPH 48H 08/1800Z 34.8N 45.4W 50 KT 60 MPH 72H 09/1800Z 31.5N 40.5W 55 KT 65 MPH 96H 10/1800Z 28.5N 35.5W 55 KT 65 MPH 120H 11/1800Z 28.5N 31.0W 55 KT 65 MPH $$ Forecaster Beven/Avila

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Hurricane Sergio Forecast Discussion Number 30

2018-10-06 22:35:32| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Oct 06 2018 000 WTPZ41 KNHC 062035 TCDEP1 Hurricane Sergio Discussion Number 30 NWS National Hurricane Center Miami FL EP212018 200 PM PDT Sat Oct 06 2018 There has been little change in Sergio's satellite presentation today. The large eye remains well defined in visible and infrared satellite imagery, but there has been a slight warming of the surrounding cloud tops since this morning. However, the latest subjective and objective satellite intensity estimates still support an initial wind speed of 110 kt. As mentioned in the previous discussion, the primary factor regarding Sergio's future intensity will be ocean temperatures beneath the cyclone over the next few days, since the other environmental conditions are expected to remain favorable. Sergio should remain over warm waters during the next day or so, but some upwelling of cooler water is possible as Sergio slows down and makes its predicted sharp turn Sunday night and Monday, and this is forecast to cause some gradual weakening during that time. After 72 hours, cooler waters, increasing southwesterly shear, and less favorable thermodynamic conditions are likely to result in additional weakening. The NHC intensity forecast lies between the higher statistical guidance and the consensus aids, and is very similar to the previous advisory. Sergio is moving west-southwestward at about 6 kt. The hurricane should turn westward tonight before making a sharp northeastward turn as a mid-level trough drops southward to the north of Sergio and erodes the western portion of the ridge. By early next week, Sergio should move northeastward ahead of the aforementioned trough. The track guidance is in good agreement on the overall scenario but there continues to be differences in the future forward speed of the hurricane. The guidance has once again trended a little slower this cycle, and the new NHC track lies between the previous forecast and the latest consensus models. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 14.6N 124.7W 110 KT 125 MPH 12H 07/0600Z 14.5N 125.7W 110 KT 125 MPH 24H 07/1800Z 14.6N 126.9W 105 KT 120 MPH 36H 08/0600Z 15.1N 127.4W 100 KT 115 MPH 48H 08/1800Z 15.7N 127.4W 90 KT 105 MPH 72H 09/1800Z 17.5N 125.6W 80 KT 90 MPH 96H 10/1800Z 20.0N 121.8W 70 KT 80 MPH 120H 11/1800Z 24.2N 116.5W 50 KT 60 MPH $$ Forecaster Brown

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Tropical Storm Leslie Forecast Discussion Number 41

2018-10-06 16:59:03| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Oct 06 2018 000 WTNT43 KNHC 061458 TCDAT3 Tropical Storm Leslie Discussion Number 41 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Sat Oct 06 2018 The central convection associated with Leslie has become better organized this morning, with conventional satellite imagery showing a tightly curved band and recent microwave imagery showing a mid-level eye. However, the microwave data also suggests the mid-level eye is located to the southeast of the low-level center. It is also not known whether there is an inner wind maximum associated with this feature. Satellite intensity estimates are mostly in the 45-55 kt range, so the initial intensity remains 50 kt. The initial motion is now 080/8. Leslie is now in or near the southern edge of the mid-latitude westerlies, and with the assistance of a couple of shortwave troughs, these are expected to push Leslie toward the east and southeast throughout the forecast period. Despite general agreement on the synoptic pattern, there is now a large spread in the guidance toward the end of the forecast period. The ECMWF and UKMET show a more southward turn after 72 h, taking Leslie well south of 30N. The GFS, on the other hand, shows a more eastward motion to the point where by 96 h it is 950 n mi from the UKMET forecast position. The new forecast track compromises between these extremes and lies near the TVCN consensus, with the caveat that the part after 72 h is of low confidence. Leslie should weaken some during the next 48 h or so as it crosses an area of cooler sea surface temperatures. After that, the track takes the center back over warmer water at the same time when there may be an increase in shear. There is an increased uncertainty in the intensity forecast caused by the track forecast uncertainties. If Leslie moves closer to the GFS track, it will be over cooler water and in stronger shear, while if it moves closer to the UKMET solution it will be over warmer water and lighter shear. Due to to the uncertainty, only minor adjustments are made to the previous intensity forecast. Additional adjustments may be needed later depending on changes in the track forecast. Large swells generated by Leslie are expected to continue during the next few days across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 37.7N 55.8W 50 KT 60 MPH 12H 07/0000Z 37.6N 54.1W 50 KT 60 MPH 24H 07/1200Z 37.3N 51.5W 45 KT 50 MPH 36H 08/0000Z 36.6N 49.0W 45 KT 50 MPH 48H 08/1200Z 35.7N 46.5W 40 KT 45 MPH 72H 09/1200Z 33.0N 41.5W 45 KT 50 MPH 96H 10/1200Z 30.0N 37.0W 50 KT 60 MPH 120H 11/1200Z 29.0N 31.0W 50 KT 60 MPH $$ Forecaster Beven

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Hurricane Sergio Forecast Discussion Number 29

2018-10-06 16:44:31| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Oct 06 2018 000 WTPZ41 KNHC 061444 TCDEP1 Hurricane Sergio Discussion Number 29 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Sat Oct 06 2018 Sergio has remained nearly steady-state since last night and the clear eye is still surrounded by very cold cloud tops. The initial intensity remains 110 kt, based on a blend of subjective and objective Dvorak intensity estimates. The primary moderating factor for Sergio's intensity over the next few days will likely be sea surface temperatures since GFS and ECMWF SHIPS diagnostics suggest that the environment will be otherwise favorable. Sergio is now moving west-southwestward at around 6 kt, likely just fast enough to outrun its own cold wake. Little change in Sergio's intensity is expected for the next day or so while the hurricane is forecast to continue moving at around this same forward speed. By early next week, a slower motion will likely cause some weakening to occur, as Sergio becomes trapped over colder upwelled waters, with further weakening likely when Sergio reaches much cooler waters to the north. The ocean-coupled regional models show more weakening than currently indicated by the official forecast, while DSHP and LGEM show a stronger storm, probably in part because those models use a constant ocean field. Confidence in the intensity forecast is not very high, and it is likely that the faster Sergio moves, the stronger it will be. The global models are in fairly good agreement on the general track of Sergio through the middle of next week, but they disagree on how quickly Sergio will move along that path. Sergio is still forecast to make a sharp u-turn toward the northeast over the next 3 days and then accelerate in that direction between 72 and 120 h. Most of the models are showing a slightly slower forward speed than earlier cycles. However there are still large differences in their representation of a shortwave trough off the coast of California that will cause Sergio's acceleration, and the model spread remains high. The new official track forecast is similar to the previous advisory but generally shows a slower speed, especially after 48 h, in line with the latest track consensus models. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 14.7N 124.0W 110 KT 125 MPH 12H 07/0000Z 14.5N 125.0W 110 KT 125 MPH 24H 07/1200Z 14.5N 126.0W 105 KT 120 MPH 36H 08/0000Z 14.9N 126.8W 100 KT 115 MPH 48H 08/1200Z 15.5N 127.0W 90 KT 105 MPH 72H 09/1200Z 17.2N 125.6W 80 KT 90 MPH 96H 10/1200Z 19.5N 122.0W 70 KT 80 MPH 120H 11/1200Z 23.6N 117.0W 50 KT 60 MPH $$ Forecaster Zelinsky

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