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Hurricane Rosa Forecast Discussion Number 12

2018-09-28 04:58:38| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Thu Sep 27 2018 270 WTPZ45 KNHC 280258 TCDEP5 Hurricane Rosa Discussion Number 12 NWS National Hurricane Center Miami FL EP202018 800 PM PDT Thu Sep 27 2018 Rosa has continued to rapidly intensify during the past several hours, with a distinct and warm eye noted on satellite images along with deep eyewall convection. A blend of the latest Dvorak estimates gives an initial wind speed estimate of 125 kt, making Rosa the seventh category 4 hurricane of the very busy 2018 eastern Pacific hurricane season. It is worth noting that this value ties 2015 for the highest observed seasonal total in the basin during the satellite era. The hurricane still has a chance to intensify further given that it is still over warm waters within light shear. By the weekend, however, Rosa will encounter more marginal SSTs, and the shear will likely increase. These conditions should cause a significant weakening of the hurricane by early next week, and for Rosa to fall back to a tropical storm by Tuesday. The intensity forecast isn't particularly confident at long range because of the possibility of a trough interaction somewhat offsetting the effects of cool eastern Pacific waters and dry stable air. So far the guidance is fairly consistent, and the forecast continues to show steady weakening as Rosa approaches Baja California. Rosa continues moving at 265 deg, now at 8 kt. A mid-level ridge over the southwestern United States is forecast to weaken and move eastward over the next couple of days as a mean mid-tropospheric trough forms near the west coast of the US. This synoptic pattern should cause the tropical cyclone to gradually turn northward over that time, and eventually move to the northeast due to Rosa getting caught up into southwestern flow ahead of the trough. While there are still some notable speed differences in the model guidance, the overall trend is for a faster solution, which is consistent with a more vertically deep system feeling the stronger mid-level flow. The model consensus continues the faster trend, and the new forecast follows suit. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 16.9N 116.7W 125 KT 145 MPH 12H 28/1200Z 17.1N 117.7W 130 KT 150 MPH 24H 29/0000Z 17.8N 118.4W 125 KT 145 MPH 36H 29/1200Z 19.0N 118.8W 115 KT 130 MPH 48H 30/0000Z 20.9N 118.8W 100 KT 115 MPH 72H 01/0000Z 25.0N 118.0W 75 KT 85 MPH 96H 02/0000Z 29.0N 115.5W 45 KT 50 MPH 120H 03/0000Z 36.0N 110.5W 25 KT 30 MPH...POST-TROP/INLAND $$ Forecaster Blake

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Tropical Storm Kirk Forecast Discussion Number 17

2018-09-28 04:47:10| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Sep 27 2018 097 WTNT42 KNHC 280247 TCDAT2 Tropical Storm Kirk Discussion Number 17 NWS National Hurricane Center Miami FL AL122018 1100 PM AST Thu Sep 27 2018 Satellite images, radar data, aircraft data, and surface observations all indicate that Kirk's center made landfall on St. Lucia around 0030 UTC. However, that fact is of minimal consequence since most of the inclement weather is displaced more than 60 n mi to the east of the center due to continued 30-40 kt of westerly shear. An Air Force Reserve Hurricane Hunter aircraft has been investigating Kirk, and SFMR winds within the convection to the east still appear to support an initial intensity of 45 kt. Since the shear affecting Kirk is not expected to abate during the next couple of days, the storm's maximum winds are forecast to gradually decrease, as is shown by all of the intensity guidance. In fact, the global models continue to insist that Kirk's circulation will open up into a trough, possibly within 24-36 hours. To maintain continuity with the previous forecast, the new NHC intensity forecast continues to show Kirk weakening to a tropical depression in 36 hours but then shows dissipation by 48 hours. Kirk's center has been moving south of due west during the past 6-12 hours, possibly due to some interaction with the mountains of St. Lucia, and the initial motion estimate is 260/10 kt. Once the center moves farther from the island, however, it is expected to resume a west-northwestward motion and increase in speed a bit as it comes under the influence of stronger ridging to its north. The NHC official forecast follows the general trend shown by the track guidance, and at least speed-wise, it is very close to the previous forecast and the HCCA model. However, given the recent motion of the center, the new forecast is nudged southward and lies south of the most reliable track models and consensus aids. Interests in the Lesser Antilles should continue to bear in mind that, although Kirk has become less organized over the past 24 hours, heavy rainfall and winds are still occurring over the eastern portion of the circulation. These winds and rains are still likely to spread westward over the islands in the Tropical Storm Warning area through early Friday. Higher winds are especially likely over elevated terrain. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 13.8N 61.4W 45 KT 50 MPH 12H 28/1200Z 14.3N 63.1W 40 KT 45 MPH 24H 29/0000Z 14.9N 65.4W 35 KT 40 MPH 36H 29/1200Z 15.3N 68.0W 30 KT 35 MPH 48H 30/0000Z...DISSIPATED $$ Forecaster Berg

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Hurricane Rosa Forecast Discussion Number 11

2018-09-27 22:49:06| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Thu Sep 27 2018 742 WTPZ45 KNHC 272049 TCDEP5 Hurricane Rosa Discussion Number 11 NWS National Hurricane Center Miami FL EP202018 200 PM PDT Thu Sep 27 2018 Rosa is undergoing rapid intensification, accompanied by the formation of a well-defined 15 n mi wide eye inside the central dense overcast. Recent subjective and objective satellite intensity estimates are generally in the 100-115 kt range, and the initial intensity is increased to 110 kt in best agreement with the CIMSS ADT and the subjective Dvorak estimate from TAFB. Rosa continues to have good cirrus outflow in all directions. The intensity forecast has some complexities. The first is how much more Rosa will strengthen before the rapid intensification stops. The new intensity forecast follows the upper edge of the guidance in showing about 12 h more strengthening with a peak intensity of 120 kt. That being said, it would not be surprising if Rosa got stronger than that. The simplest part of the forecast is from 24-72 h, when the sea surface temperatures cool along the forecast track with Rosa gradually weakening as a result. After 72 h, the cyclone should move across the quite cold waters of the northeastern Pacific, and then move across Baja California over the warm water of the Gulf of California. While that is happening, a mid-latitude trough to the northwest is expected to cause both strong shear and strong upper-level divergence over Rosa. The intensity guidance responds to this combination of ingredients with intensity forecasts of anywhere between 30-65 kt as Rosa makes landfall on the Baja California peninsula. The new intensity forecast continues to call for Rosa to weaken to a tropical storm before reaching Baja California. However, this should be considered to be a low confidence forecast at this time. Rosa is farther south than estimated in the previous advisory, and the new initial motion is now 265/9. Other than that, there is no change in the forecast philosophy from the previous forecast. For the next 12 h or so, the hurricane should move generally westward on the south side of the subtropical ridge over the Pacific west of northern Mexico and a mid-latitude ridge over California. Subsequently, Rosa should turn northwestward and northward through a break in the ridge caused by the aforementioned large mid-latitude trough moving eastward through the northeastern Pacific. By 96-120 h, Rosa should recurve northeastward into the westerlies on the eastern side of the trough and move in the general direction of the northern Baja California peninsula and northwestern Mexico. The dynamical models show spread in both direction and speed as Rosa approaches Baja. The ECMWF and the Canadian models are on the left side of the envelope in forecasting landfall on the northern part of the peninsula, while the GFS and the HWRF are on the right side with a landfall closer to the central part of the peninsula. The new forecast track lies between those extremes near the center of the guidance envelope and the consensus models. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 16.9N 115.9W 110 KT 125 MPH 12H 28/0600Z 17.0N 117.0W 120 KT 140 MPH 24H 28/1800Z 17.5N 118.1W 120 KT 140 MPH 36H 29/0600Z 18.4N 118.7W 115 KT 130 MPH 48H 29/1800Z 19.8N 119.0W 105 KT 120 MPH 72H 30/1800Z 23.5N 119.0W 85 KT 100 MPH 96H 01/1800Z 26.5N 117.0W 60 KT 70 MPH 120H 02/1800Z 31.0N 114.0W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Kirk Forecast Discussion Number 16

2018-09-27 22:35:38| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 27 2018 295 WTNT42 KNHC 272035 TCDAT2 Tropical Storm Kirk Discussion Number 16 NWS National Hurricane Center Miami FL AL122018 500 PM AST Thu Sep 27 2018 Kirk remains a sheared tropical cyclone with the exposed low-level center located to the west of the main convective mass. There has been some redevelopment of deep convection just northeast of the center this afternoon, but much of the convection is located well east and southeast of the center. Despite the satellite presentation, the Air Force Hurricane Hunter aircraft investigating Kirk through early this afternoon continued to find winds to support an initial intensity of 45 kt. Another reconnaissance aircraft mission is scheduled to fly into the storm late this afternoon and evening. The strong westerly shear that is currently affecting the tropical cyclone is forecast to increase over the next day or so, and Kirk is expected to weaken as the low- and mid-level centers decouple even further. Kirk is forecast to weaken to a tropical depression within 36 hours, and is likely to become an open trough in 2 to 3 days when the system reaches the central Caribbean Sea. The NHC intensity forecast is in good agreement with the various intensity aids, and the global models which show weakening and dissipation of the system within 72 hours. Kirk is moving west-northwestward or 290 degrees at 12 kt. A low- to mid-level ridge located over the southwestern Atlantic is expected to steer Kirk west-northwestward to westward during the next couple of days. The updated NHC track forecast is near the middle of the tightly clustered guidance, and is essentially an update of the previous advisory. Interests in the Lesser Antilles should bear in mind that, although Kirk has become less organized over the past 24 hours, heavy rainfall and winds are still occurring over the eastern portion of the circulation. These winds and rains are still likely to spread westward over the islands in the Tropical Storm Warning area later this evening through early Friday. Higher winds are especially likely over elevated terrain. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 14.2N 60.2W 45 KT 50 MPH 12H 28/0600Z 14.6N 62.2W 40 KT 45 MPH 24H 28/1800Z 15.3N 64.5W 35 KT 40 MPH 36H 29/0600Z 15.8N 66.8W 30 KT 35 MPH 48H 29/1800Z 16.1N 69.0W 25 KT 30 MPH 72H 30/1800Z...DISSIPATED $$ Forecaster Brown

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Hurricane Rosa Forecast Discussion Number 10

2018-09-27 16:54:05| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Thu Sep 27 2018 697 WTPZ45 KNHC 271454 TCDEP5 Hurricane Rosa Discussion Number 10 NWS National Hurricane Center Miami FL EP202018 800 AM PDT Thu Sep 27 2018 Rosa is becoming better organized. Conventional satellite imagery show a large area of cold cloud tops near the center, and there is a hint of an eye in the first-light visible images. Microwave imagery indicates that the eye structure underneath the overcast has become better defined, with less evidence of dry air entrainment than seen yesterday. The initial intensity has been increased to 90 kt in best agreement with the subjective Dvorak estimate from TAFB and the CIMSS ADT technique. The hurricane currently has good outflow in all directions. Conditions appear generally favorable for continued strengthening for the next 24-36 hr, and the new intensity forecast now makes Rosa a major hurricane in 12 h. It should be noted that if the current strengthening is the start of the previously anticipated rapid intensification Rosa could get stronger than the current forecast, which shows a peak intensity of 105 kt near the upper edge of the intensity guidance. After 36 h, the forecast track takes the cyclone over decreasing sea surface temperatures, and by the end of the forecast period it is expected to encounter strong southwesterly vertical shear. This combination should cause significant weakening, and Rosa is expected to be a tropical storm as it approaches the Baja California peninsula near the end of the forecast period. The initial motion is a somewhat uncertain 270/10. For the next 12-24 h, the hurricane should move generally westward on the south side of the subtropical ridge over the Pacific west of northern Mexico and a mid-latitude ridge over California. Subsequently, Rosa should turn northwestward and northward through a break in the ridge caused by a large mid-latitude trough moving eastward through the northeastern Pacific. By 96-120 h, Rosa should recurve northeastward into the westerlies on the eastern side of the trough and move in the general direction of northwestern Mexico and the northern Baja California peninsula. There remains some spread in the guidance forward speed after recurvature, with the GFS being faster than the ECMWF. The new intensity forecast is a blend of these extremes in forward speed at the 96 and 120 h points. Overall, the guidance envelope has shifted a little west since the previous advisory, and the new track is also shifted a little westward. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 17.2N 115.4W 90 KT 105 MPH 12H 28/0000Z 17.3N 116.9W 100 KT 115 MPH 24H 28/1200Z 17.5N 118.1W 105 KT 120 MPH 36H 29/0000Z 18.3N 119.0W 105 KT 120 MPH 48H 29/1200Z 19.5N 119.4W 100 KT 115 MPH 72H 30/1200Z 22.5N 119.5W 80 KT 90 MPH 96H 01/1200Z 26.0N 118.0W 60 KT 70 MPH 120H 02/1200Z 29.5N 115.5W 40 KT 45 MPH $$ Forecaster Beven

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