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Hurricane Larry Forecast Discussion Number 13
2021-09-03 22:54:48| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Sep 03 2021 000 WTNT42 KNHC 032054 TCDAT2 Hurricane Larry Discussion Number 13 NWS National Hurricane Center Miami FL AL122021 500 PM AST Fri Sep 03 2021 Over the course of the day, Larry's appearance has become more impressive. The eye has been gradually becoming better defined on visible satellite imagery as the center cloud top temperature has been warming on the infrared channel. Several microwave passes have been received since the last advisory. The most recent pass at 1900 UTC suggested the eye and surrounding eyewall convection is becoming better defined, though still weaker on the east side. 1800 UTC subjective Dvorak classifications were still both CI 4.5/77 kt from TAFB and SAB. However, the objective satellite estimates have been rising quickly, with the most recent UW-CIMSS SATCON estimate up to 84 kt. Thus, the NHC advisory intensity has been raised to 85 kt for this advisory, making Larry a category 2 hurricane. Larry's motion has remained fairly steady to the west-northwest throughout the day, at 285/14 kt. The latest track reasoning remains unchanged, with Larry being steered to the west-northwest around the southern periphery of an expansive mid-level ridge centered north of the hurricane. This ridge axis will gradually become oriented to the northeast of Larry with time, allowing the tropical cyclone to gradually gain more latitude. Because the ridge is quite large, even as its axis shifts eastward, a portion of the ridge will still remain to the north of the storm. The end result is that Larry should only slowly gain a more poleward component of motion as the system also gradually slows down. While the track guidance spread remains small for the first 48-60 hours of the forecast, a bit more longitudinal spread becomes apparent thereafter, which appears related to how much mid-level ridging remains poleward of the cyclone. The latest 12z ECMWF run has a distinctly stronger ridge, oriented more poleward in comparison to the 12z GFS run. Thus, it is not surprising to see that the ECMWF track is a bit further west and slower than the GFS. The latest NHC track forecast this cycle was also adjusted a bit slower, following the TVCN and HCCA consensus aids. However, it is interesting to note the latest 12z ECMWF ensembles are even slower than this track forecast, and future slower adjustments may be needed if these track solutions verify. It remains too soon to determine what impacts Larry may pose to the Island of Bermuda, but interests there should monitor updates in the forecast in the subsequent days. With the recent improvement in Larry's structure on satellite imagery, the hurricane may be starting another rapid intensification (RI) cycle, as suggested by the high RI probabilities given in the DTOPS guidance. However, the earlier microwave data also suggested that there were a lot of concentric bands outside of the primary eyewall, and it is not out of the question that another eyewall replacement cycle could begin in the next 24-36 hours. Instead of attempting to forecast these often stochastic processes, the latest NHC intensity forecast will instead show a healthy rate of deepening over the next several days, now taking Larry to 120 kt in 48 hours. Afterwards, there still remain questions as to how much the vertical wind shear will increase over Larry, with the ECMWF-SHIPS indicating higher shear that could affect Larry's inner-core structure, while the GFS-SHIPS showing much lower shear. Warmer sea-surface temperatures also await the hurricane in the 60-96 hour period. Due to these competing factors, the intensity forecast during this period will only show very gradual weakening. The latest NHC intensity forecast remains on the high end of the guidance, but still remains lower than the higher HAFS-B and COAMPS-TC models. It should be noted that the majority of the guidance also shows Larry becoming a very large hurricane, with a significant expansion of the 34-, 50-, and 64-kt wind radii also forecast. Significant ocean swells generated by the increasingly large wind field of Larry are expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and high surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 15.0N 42.0W 85 KT 100 MPH 12H 04/0600Z 15.8N 44.1W 95 KT 110 MPH 24H 04/1800Z 16.9N 46.5W 105 KT 120 MPH 36H 05/0600Z 18.1N 48.7W 110 KT 125 MPH 48H 05/1800Z 19.4N 50.8W 120 KT 140 MPH 60H 06/0600Z 20.7N 52.8W 120 KT 140 MPH 72H 06/1800Z 21.9N 54.5W 115 KT 130 MPH 96H 07/1800Z 24.7N 57.6W 115 KT 130 MPH 120H 08/1800Z 28.7N 60.5W 105 KT 120 MPH $$ Forecaster Papin
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Hurricane Larry Forecast Discussion Number 11
2021-09-03 10:33:37| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Sep 03 2021 000 WTNT42 KNHC 030833 TCDAT2 Hurricane Larry Discussion Number 11 NWS National Hurricane Center Miami FL AL122021 500 AM AST Fri Sep 03 2021 Larry continues to gradually become better organized. Satellite images show a fairly compact central dense overcast feature with an eye occasionally evident. Beyond the inner core, banding features are gradually becoming more distinct, especially to the south of the center. The latest Dvorak classifications at 0600 UTC was 4.5/77 kt from TAFB and SAB, and based on those estimates and the improving trend, the initial intensity is nudged upward to 80 kt. Larry is moving west-northwestward at 17 kt. There has been no change to the track forecast reasoning. A continued westward to west-northwestward motion is expected on Friday and through the weekend as the hurricane remains on the south side of a mid-level ridge. By early next week, Larry is expected to slow down and turn northwestward when it reaches the southwestern periphery of the ridge. The models are in fairly good agreement, and the NHC track forecast lies near the middle of the guidance envelope. This forecast is largely an update of the previous one. The environmental factors appear favorable for steady strengthening during the next few days with wind shear remaining low and mid-level moisture fairly high. The only slightly negative factor is marginally warm 26-27 deg C waters that Larry will be moving over during the next couple of days, which should prevent rapid intensification. All of the models are in general agreement that Larry will become a major hurricane in a day or so with continued strengthening through day 3, and the NHC intensity forecast follows suit. Some weakening is shown by the end of the forecast period when the wind shear could increase a little. This forecast is very similar to the previous one and lies near the high end of the guidance envelope. It should be noted that eyewall replacement cycles are possible, which could cause intensity fluctuations that are challenging to predict. The leading swell front from Larry is expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and high surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 14.6N 38.9W 80 KT 90 MPH 12H 03/1800Z 15.2N 41.1W 90 KT 105 MPH 24H 04/0600Z 16.2N 43.8W 100 KT 115 MPH 36H 04/1800Z 17.3N 46.2W 105 KT 120 MPH 48H 05/0600Z 18.6N 48.5W 115 KT 130 MPH 60H 05/1800Z 19.8N 50.5W 120 KT 140 MPH 72H 06/0600Z 21.1N 52.5W 120 KT 140 MPH 96H 07/0600Z 23.8N 55.8W 115 KT 130 MPH 120H 08/0600Z 27.1N 58.9W 110 KT 125 MPH $$ Forecaster Cangialosi
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Hurricane Larry Forecast Discussion Number 10
2021-09-03 04:33:58| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Sep 02 2021 000 WTNT42 KNHC 030233 TCDAT2 Hurricane Larry Discussion Number 10 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Thu Sep 02 2021 A series of SSMIS microwave passes earlier this afternoon indicated that Larry may have been starting an eyewall replacement. However, the last pass at 2058 UTC suggested that the eyewall replacement failed, with the western part of the outer eyewall being eroded, possibly by some modest mid-level shear and some dry air, and the tighter inner eyewall trying to re-establish itself. As a result, the convective pattern has reverted back to a small Central Dense Overcast. Subjective Dvorak intensity estimates are now T4.5/77 kt from TAFB and T4.0/65 kt from SAB, and the latest objective estimates range from 72 to 78 kt. Overall these numbers have risen a bit, and Larry's maximum winds are now estimated to be 75 kt. Larry continues moving toward the west but perhaps slightly faster (280/17 kt). There is no change to the track forecast reasoning. A fairly stagnant pattern consisting of a strong mid-level high over the central Atlantic and broad-scale troughing over the eastern United States and western Atlantic should persist through the 5-day forecast period. Larry is therefore forecast to turn toward the west-northwest on Friday and then take on a northwest heading Sunday through Tuesday while it moves around the southwestern periphery of the high. The updated NHC track forecast lies right along the previous forecast and is very close to the various consensus aids. Low shear, gradually increasing sea surface temperatures, and the potential for an upper-level outflow jet to form north of the hurricane during the next 24-48 hours should support continued strengthening. During the first 48 hours, the NHC forecast shows a steady increase of 10 kt every 24 hours, close to the HCCA consensus aids and near the top of the guidance envelope. By days 3 and 4, there continue to be indications that increasing westerly or northwesterly shear could become a factor, and the NHC forecast therefore shows a leveling off of the intensity, with some slight weakening by the end of the forecast period. If Larry becomes a strong hurricane, eyewall replacements would also be a possibility, which would likely lead to difficult-to-forecast fluctuations in intensity. The leading swell front from Larry is expected to reach the Lesser Antilles on Sunday, increasing the risk of life-threatening rip currents and surf conditions on those islands early next week. Large swells are likely to spread to areas surrounding the western Atlantic later in the week as well. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 14.1N 37.5W 75 KT 85 MPH 12H 03/1200Z 14.5N 39.9W 85 KT 100 MPH 24H 04/0000Z 15.3N 42.6W 95 KT 110 MPH 36H 04/1200Z 16.4N 45.2W 105 KT 120 MPH 48H 05/0000Z 17.6N 47.5W 115 KT 130 MPH 60H 05/1200Z 19.0N 49.7W 120 KT 140 MPH 72H 06/0000Z 20.4N 51.8W 120 KT 140 MPH 96H 07/0000Z 22.9N 55.0W 115 KT 130 MPH 120H 08/0000Z 25.9N 58.0W 110 KT 125 MPH $$ Forecaster Berg
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Hurricane Larry Forecast Discussion Number 9
2021-09-02 22:49:53| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Sep 02 2021 000 WTNT42 KNHC 022049 TCDAT2 Hurricane Larry Discussion Number 9 NWS National Hurricane Center Miami FL AL122021 500 PM AST Thu Sep 02 2021 This afternoon, Larry's appearance has evolved from a small central dense overcast to a tightly coiled spiral banding pattern, with these bands wrapping into the estimated center. I finally received a useful SSMIS microwave overpass at 1857 UTC which provided evidence that Larry could be undergoing an eyewall replacement cycle (ERC). The imagery suggests a large outer eyewall is taking shape on the low-level 37-GHz channel, while an inner eyewall fragment is still seen on the mid-level 91-GHz channel. Despite these structural changes, the 1800 UTC subjective Dvorak estimates from TAFB and SAB were unchanged from this morning at CI 4.0/65 kt. In addition, the latest objective intensity estimates from SATCON and ADT have only varied slightly at 73 kt and 74 kt respectively. Taking a blend of the subjective and objective estimates still yields 70 kt for this advisory. Larry continues to move just north of due west, with the latest motion estimated at 280/16 kt. There is not much new to report with the track reasoning, with a large mid-level ridge currently north of Larry expected to steer the hurricane to the west or west-northwest over the next 2-3 days. Over time, the ridge axis is forecast to slowly shift further northeast of Larry's position, allowing the hurricane to gradually gain a more rightward component of motion by the end of the forecast period. In general, the track guidance remains tightly clustered for the first 2-3 days. There was a notable shift west in the latest 12z GFS deterministic track, while the 12z ECMWF shifted ever so slightly right. A quick look at the 12z ECMWF ensemble guidance reveals that the deterministic run is a bit to the northeast of the ensemble mean. The latest NHC track has been shifted slightly to the south and west of the previous track, following the reliable HFIP corrected consensus aid (HCCA) which also shifted a bit south and west this cycle. Once Larry completes the ongoing ERC, significant or even rapid intensification is anticipated. The short-term intensity forecast has been raised a bit more, since it appears more likely the present ERC will finish in the next 6-12 h. The latest NHC intensity forecast now makes Larry a major hurricane by tomorrow night, with further intensification up to Category 4 intensity anticipated by Sunday. Once again, there remains some discrepancy in the vertical wind shear forecast between the GFS- and ECMWF-based SHIPS guidance, with the ECMWF forecasting significantly more southwesterly shear beyond 72 hours. Both guidance tools also indicate a decrease in mid-level relative humidity which, if the shear materializes, could disrupt Larry's inner core structure. Thus, the NHC intensity forecast still shows gradual weakening from 72 to 120 hours. The latest intensity forecast is just a hair above HCCA in the short term, with the intensity forecast most closely following the latest COAMPS-TC (CTCI) guidance in the first three days. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 13.7N 35.8W 70 KT 80 MPH 12H 03/0600Z 14.0N 38.4W 80 KT 90 MPH 24H 03/1800Z 14.7N 41.3W 95 KT 110 MPH 36H 04/0600Z 15.7N 43.9W 105 KT 120 MPH 48H 04/1800Z 16.9N 46.3W 110 KT 125 MPH 60H 05/0600Z 18.3N 48.6W 120 KT 140 MPH 72H 05/1800Z 19.7N 50.6W 120 KT 140 MPH 96H 06/1800Z 22.2N 54.0W 115 KT 130 MPH 120H 07/1800Z 25.1N 57.0W 110 KT 125 MPH $$ Forecaster Papin
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Hurricane Larry Forecast Discussion Number 8
2021-09-02 16:51:18| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 02 2021 000 WTNT42 KNHC 021451 TCDAT2 Hurricane Larry Discussion Number 8 NWS National Hurricane Center Miami FL AL122021 1100 AM AST Thu Sep 02 2021 Larry continues to gradually become better organized this morning, with a small but cold CDO near the estimated center, and well defined curved bands rotating completely around. Unfortunately, there have not been any recent microwave passes over the center in the last 6-9 hours. However, I did receive a helpful ASCAT-B pass at 1128 UTC which indicated that while the inner core remains quite small, the 34-kt wind radii have expanded dramatically in all quadrants. The most recent Dvorak subjective intensity estimates were both CI 4.0/65 kt from SAB and TAFB. However, the objective intensity estimates from SATCON and ADT are higher, at 70 kt and 77 kt respectively. Thus, the current intensity of Larry was nudged upward to 70 kt for this advisory. The hurricane's heading has changed little this morning, estimated at 280/15 kt. There also remains little change to the forecast track reasoning. A dominant mid-level ridge is located north of Larry and should maintain the hurricane on a west to west-northwest heading over the next 72 hours. The track guidance is in excellent agreement over this time period. After 72 hours, a bit more track guidance spread begins to take shape, which appears related to the evolution of the the steering ridge orientation. For example, the most recent GFS run begins a more pronounced rightward bend, as the ridge becomes positioned northeast of the tropical cyclone. In contrast, the ECMWF and a number of its left-leaning ensemble members maintain more ridging directly north of Larry, keeping the hurricane on a more leftward track with only a gradual bend to the west-northwest and northwest. These differences notwithstanding, the consensus aids has changed little from the previous forecast cycle, and the NHC forecast track is nearly identical to the previous track. This track lies very close to the HCCA consensus aid, which favors a track solution a bit closer to the ECMWF versus the GFS. Larry's environmental conditions appear very favorable for additional intensification over the next 60-72 hours. In fact, the primarily forecast challenge relates to how Larry's core structure evolves over the next several days. Right now, the inner-core and hurricane-force wind radii are very small relative to the expanding tropical-storm-force wind field around the storm. Thus, it appears likely that Larry will undergo some form of an eyewall replacement cycle (ERC) in the next 12 to 24 hours, which may slow down the short term intensification rate. However, once this cycle is complete, very light easterly vertical wind shear between 2-8 kt, abundant mid-level moisture, and sufficently warm sea-surface temperatures between 27-28 C should favor steady to rapid intensification. The latest NHC intensity forecast now calls for a peak intensity of 120 kt in roughly 72 hours, which is a faster and slightly higher peak than the prior forecast. Afterwards, the guidance is a bit conflicted. The GFS-based SHIPS continues to suggests low vertical wind shear through the end of the forecast period. However, the ECMWF-based SHIPS shows much higher southwesterly vertical wind shear beginning in 84 hours as Larry also moves into a drier environment. It is also possible additional ERCs may occur in the latter portion of this forecast, resulting in additional intensity fluctuations. For these reasons, the intensity forecast at the end of the period shows some modest weakening. This intensity forecast is a bit higher than the HCCA corrected consensus aid, but remains lower than some of the more aggressive guidance (COAMPS-TC, the experimental HAFS-B). FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 13.5N 34.2W 70 KT 80 MPH 12H 03/0000Z 13.8N 36.7W 75 KT 85 MPH 24H 03/1200Z 14.4N 39.7W 85 KT 100 MPH 36H 04/0000Z 15.3N 42.6W 95 KT 110 MPH 48H 04/1200Z 16.5N 45.2W 105 KT 120 MPH 60H 05/0000Z 17.9N 47.6W 115 KT 130 MPH 72H 05/1200Z 19.2N 49.7W 120 KT 140 MPH 96H 06/1200Z 21.8N 53.1W 115 KT 130 MPH 120H 07/1200Z 24.6N 56.0W 110 KT 125 MPH $$ Forecaster Papin
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